Few buildings in Hamburg feature such a jarring contrast between hulking, Brutalist concrete and lush greenery. This bunker started life in 1942 as part of the eight Flak towers, built during World War II to defend major German cities. These were largely the initiative of Adolf Hitler himself, who provided input into the initial designs. The towers were considered such a priority that Germany’s railways were ordered to prioritize necessary construction shipments.

Built primarily for anti-aircraft defense, one tower could provide a rate of fire of 8,000 rounds per minute with an 360-degree range of 14 kilometers. They also contained retractable radar installations and could double as air raid bunkers with a capacity of 10,000 people. A staggering 30,000 civilians crammed inside one during the Battle of Berlin.

Although the Flak towers did not prevent cities from being intensely bombed by the Allies, their 3.5-meter-thick walls were so impenetrable that even the largest Soviet guns could do little damage. Following the war, some towers were not demolished because of the difficulty of doing so. The required explosives could have caused damage as far as two kilometers away.

In the case of the Feldstraße Bunker, the auxiliary L-Tower used for communication and fire control was eventually demolished but the main G-Tower remained. It is the only surviving intact G-Tower of the first-generation design, consisting of a castle-like structure with four octagonal turrets.

Immediately after the war, this Flak tower was used as emergency housing, since most of the city’s homes were damaged by bombing the tower failed to prevent. In the early 1950s, it continued to be used as temporary housing for victims of domestic abuse. It also continued to be used as a potential bomb shelter due to the Cold War. In the 1990s, the bunker was repurposed as a center for different media businesses, including a concert hall, advertisement agencies, nightclub, and a musical instrument store. 

The idea of “greening” the bunker by adding plants on the exterior was first proposed in 1992, however the idea did not get off the ground until architect Mathias Müller-Using managed to attract investors to it in the 2010s. They added five stories to the building, which would be used as a hotel with restaurants, and event hall, and a fitness club. Criticisms were initially levied because the greenery had to be scaled back due to fire codes and the land was leased at a discount. The “green bunker” was finally completed in 2024 after two years of delay. It is open to all and has a rooftop garden and a “mountain path” panoramic staircase on the side.