Camp Century was built underneath the surface of the Greenland Ice Sheet in 1959 by the the US Army Corps of Engineers

the project was designed to create a network of mobile nuclear missile launch sites in Greenland, almost an entire underground city, with bars, theaters and other buildings

https://www.militarytimes.com/off-duty/military-culture/2023/12/13/inside-the-us-armys-failed-nuclear-lair-in-cold-war-greenland

https://www.motherjones.com/environment/2017/06/camp-century-global-warming

https://www.thedrive.com/news/this-massive-1960s-off-road-overland-train-has-a-kitchen-beds-bathroom-inside