The Hochbunker in Hamburg’s St. Pauli district, a WWII flak tower, has been transformed into a 'green mountain' with extensive gardens on its roof. Originally built in 1942 to shelter up to 18,000 people, the bunker avoided demolition due to its structural integrity and was repurposed for various uses over the decades. 

The recent restoration, driven by the Hilldegarden eV association, includes restaurants, event spaces, a hotel, and a rooftop park with a 'mountain path' and 80 sensors to study green roofs and facades’ impact on the microclimate. 

Opened on July 5, 2025, it features a memorial for Nazi victims and aims to be a model for climate-resilient urban spaces. This project parallels other global efforts to repurpose historical structures while preserving their significance.