Underwater habitat 'Helgoland'

The 'Helgoland' underwater laboratory (UWL), built in Lübeck in 1968, was the first of its kind in the world built for use in colder waters.

The 14 m long, 7 m wide and 7 m high UWL meant that divers were able to spend several weeks under water. The scientists and technicians would live and work in the laboratory, returning to it after every diving session. Only once they had reached the end of their stay did they decompressed in the UWL itself, being able to then resurface without coming to any harm.
The UWL was used in the waters of the North and Baltic Seas as well as on the east coast of the USA. At the end of the 1970s it was decommissioned.