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Berliner Unterwelten

Berlin's underground world contains an almost invisible part of the city's history. Beneath streets, squares and buildings are bunkers, air-raid shelters, tunnels, abandoned railway facilities, utility installations and other structures that tell the story of some of the most dramatic periods in Berlin's history.

One of the organisations that has worked for more than a quarter of a century to investigate, document, preserve and communicate this history is Berliner Unterwelten e.V. The association was founded in 1997 and has developed from a small group of people interested in Berlin's underground into a comprehensive organisation with research, historical projects, exhibitions, lectures, publications and guided tours.

For me, Berliner Unterwelten is particularly interesting because the association's work connects visible history with the history hidden beneath the city. It is precisely underground that many traces of Berlin during the Second World War, National Socialism, the Cold War and the divided city can still be found.

Dietmar Arnold – a childhood fascination with Berlin's underground

Presenter and journalist Sabine Heinrich and Dietmar Arnold, chairman and co-founder of Berliner Unterwelten.

The history of Berliner Unterwelten is closely connected with Dietmar Arnold, who has been one of its central figures since the association was founded and has served as chairman since 1997.

Arnold's fascination with Berlin's underground began when he was already a teenager. In 1979, he and a group of friends decided to explore the remains of the enormous underground bunker complex beneath the former flak tower in Humboldthain.

The boys had heard stories about the enormous underground complex and about a possible underground lake. Equipped with folding shovels, flashlights, packed lunches and a rubber boat, they entered the remains of the bunker through a partially blocked entrance.

They crawled through narrow passages, climbed over collapsed concrete and moved through several underground levels. Among other things, they found abandoned equipment, radio components and other objects from the war.

The adventure was not without danger. Among the finds were ammunition magazines and Panzerfaust weapons. Eventually, the authorities became involved, and the entrance was later sealed with concrete. The expeditions thus came to an end, but the experience stayed with Arnold.

Many years later, he returned to Berlin's underground world – this time professionally, as a surveying technician and urban planner. In 1997, he became a co-founder of Berliner Unterwelten e.V.

The story of Dietmar Arnold shows in a particularly striking way how a youthful fascination with forgotten places developed into systematic historical research, documentation and preservation work.

The remains of the former flak tower in Friedrichshain, Berlin.

Read also my page about Flakturm Humboldthain – the Second World War bunker complex.

Berliner Unterwelten founded in 1997

The association was established in Berlin in 1997 among people who shared an interest in the city's underground structures and their history.

The first recorded meeting between twelve people interested in Berlin's underground took place on 25 April 1997. A formal founding general meeting followed on 12 June 1997, when the first board was elected. The association's statutes were adopted on 19 June, and Berliner Unterwelten e.V. was officially registered in the register of associations on 5 December 1997.

From the beginning, the work was not merely about exploring underground spaces. An equally important goal was to preserve and document historical structures that were threatened by demolition, filling, new construction or simply being forgotten.

In 1998, among other things, the association began working to have the shelters beneath Gesundbrunnen assessed with a view to their preservation as protected historic sites. This was an important step in the development from underground exploration towards systematic preservation work.

The association's purpose

Berliner Unterwelten e.V. is a non-profit association. Its purpose includes research and education, art and culture, as well as the preservation and protection of historic structures and cultural heritage.

In practice, this means that the association works with far more than guided tours. Members investigate historic sites, examine archival material, collect photographs and documents, record finds, restore buildings and objects, and communicate the results through exhibitions, books, lectures and guided tours.

Research into Berlin beneath the surface

Berliner Unterwelten does not merely investigate underground structures as isolated attractions, but seeks to understand them within their historical and social context.

The research includes, among other things, air-raid protection, Second World War bunkers, flak towers, underground transport systems, tunnels, industrial facilities, weapons production and Cold War installations.

Another important area is the connection between the various structures. Berlin's underground is not simply a collection of individual bunkers. Beneath the city there was a network of railways, U-Bahn lines, utility tunnels, sewers, communication links, shelters and other technical installations.

The association therefore also works with the broader connection between the city above ground and the city below ground.

Berliner Unterwelten – the work of exploring Berlin's hidden underground history.

The underground under National Socialism

When examining Berlin's underground structures, they cannot be separated from the political history that created many of them. Under National Socialism, Berlin was expanded as the centre of the German dictatorship, and the plans for the so-called Welthauptstadt Germania involved enormous changes to the city.

At the same time, shelters, technical installations and connections to important governmental and military functions were established underground. Some of these sites are today among the most important physical sources for understanding Berlin during the Nazi era.

Berliner Unterwelten works, among other things, with the history of the bunker complexes in the area around the former government district, Wilhelmstraße and the Führerbunker.

At the same time, it is important to emphasise that these places tell us more than just about architecture and technology. They also tell us about a dictatorship, warfare, forced labour, persecution and the human consequences of National Socialism.

The association's exhibition Hitlers Pläne für Berlin: Mythos Germania addresses precisely this connection between the monumental building plans and the crimes that were a prerequisite for their implementation.

On my own page about Berlin during the war, you can read more about the city, the bombing raids and the development of the war.

Bunkers, air-raid protection and the Second World War

The Second World War significantly changed Berlin's underground landscape. After the first British bombs fell on Berlin in August 1940, work on air-raid protection was intensified. Later, a large number of different bunker and shelter facilities were built throughout the city.

Some were relatively small shelters, while others were massive reinforced-concrete structures. There were high-rise and low-rise bunkers, factory bunkers, hospital bunkers, railway and U-Bahn facilities, as well as shelters associated with public institutions.

At the same time, parts of the existing underground infrastructure were put into use to protect the population. U-Bahn stations, cellars and other underground spaces thus became an important part of the civilian population's ability to seek shelter during bombing raids.

A good example is Flakturm Humboldthain, where both the enormous above-ground flak tower and the extensive underground structures tell the story of Nazi Germany's air defence.

Another example is Hochbunker Pallasstraße, which shows how bunker architecture later became part of modern Berlin.

The Tempelhof Airport also contains an important underground history. During the Second World War, parts of the complex were used for armaments production, and beneath the large buildings there is an extensive system of technical and underground installations.

Berlin 1945 – destruction and downfall

In the final months of the war, Berlin was transformed into a battlefield. Bombing raids, artillery fire and the fighting during the Soviet offensive in April and May 1945 destroyed large parts of the city.

For the people who were in Berlin, the bunkers became some of the last places where they could seek protection. An important part of the final days of the Nazi regime therefore unfolded underground.

The bunkers also illustrate the contrast between official Nazi propaganda and the reality experienced by the civilian population. On the surface there was the belief in the coming victorious Germany, while people underground experienced bombing, shortages of food and water, fear, chaos and ultimately the collapse of the regime.

Today, some of these authentic sites are used to communicate precisely this final phase of the war. Berliner Unterwelten organises, among other things, lectures and commemorative events in which personal accounts and historical sources are included.

The post-war period and the Cold War

After 1945, many of Berlin's bunkers acquired a new history. Some were blown up, while others were partially destroyed, filled in or sealed. Still others were given completely new functions.

A particularly interesting example is the Fichtebunker in Kreuzberg. The former gasometer was converted into a large shelter during the Second World War. After the war, the building was used, among other things, to accommodate refugees, as a juvenile detention centre, an old people's home and later as an emergency reserve facility.

These changes in use show that Berlin's underground structures did not end their history in 1945. They continued to form part of the city's development.

During the Cold War, many facilities acquired yet another function. West Berlin developed civil-defence and nuclear emergency facilities, while East Berlin and the GDR developed other forms of protection and military infrastructure.

On my page about the Stasi Museum, you can see another part of the history of the GDR and the East German security apparatus, while the page about Karlshorst tells the story of the place where the German surrender was signed on 8 May 1945.

The Berlin Wall and the escape tunnels

When the Berlin Wall was erected in August 1961, it also changed the underground world. Suddenly, tunnels and basement rooms could become a possible route to freedom.

Numerous escape attempts were made through tunnels from East Berlin to West Berlin. Some tunnels were built by professional escape helpers, others by families or small groups. Several were discovered by the GDR security apparatus, while others succeeded.

For many years, Berliner Unterwelten has researched these tunnels and collected information from former escape helpers and other contemporary sources.

Read also my page about the escape tunnels between East and West Berlin, where this dramatic part of the Cold War history is discussed in greater detail.

Bernauer Straße is also closely connected with the underground escape history. The area became one of the most dramatic places along the Berlin Wall, and tunnels were dug here and spectacular escape attempts were carried out.

Another central location is Bornholmer Straße, where the border crossing was opened on 9 November 1989, making it a symbol of the collapse of the Wall.

Read also my comprehensive page about the Berlin Wall.

Reunification and the rediscovery of the underground

After the fall of the Wall and German reunification in 1990, large parts of Berlin were transformed. Areas that had been inaccessible for decades were opened up, demolished or redeveloped.

At the same time, many previously secret or forgotten underground structures were rediscovered. These included shelters, tunnels and technical installations that had been hidden beneath the divided city.

For Berliner Unterwelten, this development created an opportunity to work more systematically with the historic sites. Many facilities could be investigated, documented and, in some cases, made accessible to the public.

It is also here that the association's work takes on particular significance. Once an old underground structure has been demolished or filled in, it can be very difficult – and often impossible – to reconstruct its original form.

Preservation rather than glorification

The preservation of wartime bunkers raises difficult questions. Many of the structures are directly connected with National Socialism, the war, forced labour, weapons production and the destruction of Berlin.

It is therefore important that preservation does not become a glorification of the bunker itself or of the regime that had it built. A historic site must be capable of being examined and explained critically.

Berliner Unterwelten regards the preserved structures as historical sources. The aim is to understand what they were built for, who built them, who used them and which people were affected by the systems of which they formed part.

For precisely this reason, in my opinion, it is important to preserve some of these places. An authentic bunker can tell the story in a different way from a museum built from scratch or a modern reconstruction.

The underground as a historical source

A glimpse into Berlin's underground world, which is investigated and documented by Berliner Unterwelten.

One of the strengths of Berliner Unterwelten is the combination of historical research and direct investigation of the preserved structures.

Building plans, photographs, archival material and contemporary accounts can be compared with the physical remains beneath the city. In this way, parts of Berlin's history can be reconstructed even when they can no longer be seen on the surface.

This applies, for example, to investigations of former bunker complexes, where newer construction or other changes to the city have made it necessary to combine old documents with archaeological and technical investigations.

A good example is the work on the escape tunnels from the divided city. Here, even small remnants of a tunnel, an entrance or a technical installation can be valuable because they can be compared with the accounts, photographs and documents that already exist.

For researchers interested in Berlin during the Second World War and the Cold War, this combination of documentary and physical material is particularly valuable.

Guided tours, exhibitions and public outreach

Today, Berliner Unterwelten combines research and preservation with public outreach. The association organises guided tours, exhibitions, educational activities, lectures, cultural events and publications.

The association's facilities at Gesundbrunnen are the centre of many of its activities. Several guided tours of Berlin's underground structures start from here, and exhibitions about the city's history are also located here.

In 2025, the association recorded more than 326,000 visitors to its guided tours. In addition, there were visitors to exhibitions, seminars, lectures and various events. This shows that interest in Berlin's underground history remains very strong.

Volunteers are also an important element. Large parts of the work involving maintenance, documentation, events and historical research are carried out with the help of the association's members.

Gesundbrunnen – the headquarters of Berliner Unterwelten and the starting point for several of the association's guided tours.

Members, volunteers and support

Berliner Unterwelten is not simply a company that organises tourist tours. It is an association in which its members play an important role in the practical work.

According to the most recently published annual report, there were 580 members. The association therefore continued to have a growing membership after the years of the coronavirus pandemic, when many activities had been more difficult to carry out.

Members can, among other things, participate in working groups dealing with research, exhibitions, documentation, events, information and maintenance of the facilities. This means that the association is to a significant extent dependent on people who are willing to devote their free time to the work.

A good example is the work in the Adlon bunker, where members have helped remove large quantities of rubbish and debris. During work in September 2025, 21 members took part and removed more than 12 tonnes of material from the facility.

In my opinion, this form of voluntary work is one of the most interesting aspects of Berliner Unterwelten. The association is able to turn historical interest into concrete preservation work.

Berliner Unterwelten in 2025 and 2026

The past few years show that Berliner Unterwelten continues to develop.

In 2025, the association, among other things, received usage rights to several flak bunkers in Tempelhof and continued its work on restoration and documentation. The same year saw a large number of events, and the association recorded 326,647 visitors on 15,540 guided tours.

In 2026, the work has continued. Among other things, the association has opened a new guided tour in the former nuclear shelter beneath Pankstraße, where the history of civil defence during the Cold War is connected with contemporary questions concerning emergency preparedness and the protection of the civilian population.

This is interesting because the history of the underground is therefore no longer only about the past. It is also being used to discuss today's security policy situation.

Another major project is the Adlon bunker beneath Pariser Platz. After the complex was able to reopen in 2024 following almost 30 years under water, the association has been working on securing, cleaning and documenting the site. In the longer term, the aim is to make the facility more accessible and create an exhibition and educational presentation about the bunkers in the former government district.

In 2026, a serious discussion has also arisen about the continued existence of the large bunker beneath the area of the former Neue Reichskanzlei. Berliner Unterwelten has publicly argued against demolition and in favour of preserving the underground structure so that it can form part of a future information, educational and documentation centre about the final days of the Nazi regime.

At the same time, the association has argued that preserving the bunker does not necessarily have to prevent a new construction project on the site. It is precisely these kinds of conflicts that may become decisive in the coming years for how much of Berlin's underground history will actually survive.

The challenges ahead

Berliner Unterwelten is today facing a number of challenges. The most important, in my view, is the question of what should be preserved and what must give way to urban development, new construction and modern infrastructure.

Berlin is a city in constant change. Sites where bunkers and other underground structures are located can become attractive areas for development. Once a structure has been removed or filled in, the historical source is in many cases lost forever.

The case of the bunker beneath the area of the former Neue Reichskanzlei clearly demonstrates this conflict between urban development and preservation. Berliner Unterwelten believes that authentic historic sites cannot be replaced by reconstructions.

Another challenge is finance. Many facilities require extensive cleaning, securing, technical maintenance, drainage, documentation and restoration. The work on the Adlon bunker demonstrates how extensive such a task can be.

There is also a very practical challenge. Many underground structures are difficult to make accessible to people with reduced mobility. Stairs, narrow passages, uneven floors and technical conditions often make full accessibility difficult. Berliner Unterwelten has, however, already shown that progress is possible. The OP bunker on Teichstraße became the first of the association's facilities in 2024 to be made fully physically accessible with a wheelchair ramp.

A third challenge is the generational transition. A large part of the personal knowledge about the war, the GDR, the escape attempts and the divided city comes from people who experienced these events themselves. As these witnesses gradually become fewer, it becomes increasingly important to document their stories while this is still possible.

Here, the association's archive, research work and cooperation with former escape helpers and other contemporary witnesses play an important role.

Finally, there is the question of interest among future generations. The fact that more than 326,000 people took part in the association's guided tours in 2025 demonstrates a very high level of interest, but historical communication must constantly evolve if it is to remain relevant.

Why Berliner Unterwelten is important to my research

Berliner Unterwelten is of particular interest to my own research into Berlin's history during the Second World War and the former Danish Legation.

The association's work with bunkers, air-raid protection and underground structures provides an important basis for comparison in understanding the protection systems that existed around Berlin's diplomatic and governmental institutions during the Second World War.

This also applies to the former Danish Embassy in Berlin, which forms part of my own documentation of the Danish connections to Berlin during the war.

At the same time, Berliner Unterwelten is interesting because the association works with precisely the kind of historical traces that can easily disappear from the surface. A building may have been demolished, a bunker may have been concealed, and a tunnel may have been filled in – but the physical remains can still contain information that does not exist in the written sources.

In this context, my page about Schwerbelastungskörper is also relevant, because it shows how the gigantic construction plans for Nazi Berlin also left physical traces in the city.

In the same way, my pages about Tempelhofer Park and the former Tempelhof Airport, Teufelsberg and Tempelhof Airport can be seen as parts of the larger history of how Berlin's military and technical landscape was transformed before, during and after the Second World War.

Berliner Unterwelten e.V. – contact and website

Berliner Unterwelten.

Berliner Unterwelten e.V.
Brunnenstraße 105
13355 Berlin

Official website: www.berliner-unterwelten.de

The association's website provides information about guided tours, exhibitions, research, membership, current projects and opportunities to support the work.