Berlin reinvented itself time and again throughout Germany’s history, going from a city united to a city divided and back again. Its role as the Nazi nerve center in World War II left a major impact on the country’s history, but Berlin eventually evolved into a cultural hot spot for Europe.

Above ground, the neatly organized city touts many well-preserved landmarks of its checkered past such as Checkpoint Charlie and the Brandenburg Gate. But sites like these present only half the story. Below ground, a whole world awaits where more than 130 years of the city’s history has been preserved.

Underground tours offer a popular way to explore cities around the world, providing unique glimpses at rarely seen sites like catacombs and smuggler tunnels. But in Berlin, tours of the city’s underworld give you a firsthand look at remnants of World War II and the Cold War, providing a testament to human perseverance and survival. Berlin is laid out in a well-organized fashion with wide boulevards.

Underground, however, you’ll find remnants of a time long gone that was rattled by war. What awaits is a web of escape tunnels dug by countless citizens of East Germany attempting to escape to the West during the Cold War. Another important highlight is one of the few remaining underground air raid bunkers used to keep citizens safe during the bombing of Berlin in World War II, which destroyed nearly 80 percent of the city center.

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The only way to see this side of Berlin is by taking part in a guided tour. Most tours start at the Berlin-Gesundbrunnen subway station, where the offices of the Berliner Unterwelten E.V. (Berlin Underworlds Association) are located within a former air raid shelter. This company has worked since 1997 to uncover and preserve this unique perspective of Berlin’s history and has shared it with the public since 1999.

These underground tours offer a rare glimpse into life in Berlin during World War II and the Cold War that followed, but it also delves into other aspects of the city’s history you’re unlikely to hear about elsewhere. These include the gasometer system that once lit the city’s streetlights from below ground, and the tube post system, known as the Rohrpost, that used a pneumatic tube network to deliver mail and telegrams across Berlin.

These tours will give you a picture of the city that spans more than a century; and when you pair an underground exploration with the incredible attractions above ground, you will gain a different perspective on the city’s personality and the resilience of its people.