Maybe of interest for some of you:
Fuchsbau was erected by the SS as its main telephone switch central and in working condition at the end of the war, afterwards abandoned, then taken into service again by East German airforce as the main aircontrolcenter, widely enlarged with a new three level command center connected to the old part and 1990 the west German army took it over for just three years until it was sealed with concrete and reopened by some bunker nerds in 2005.
https://www.bunkermuseum-fuchsbau.de/
Enjoy the images