The Poles built this in 1939 in anticipation of WWII. They never got to use it, but the invading Germans did as an air raid shelter and observation post. Post-war the Poles continued to think of it as a possible defensive point, but by 1970 abandoned the notion, and turned it over to civilian control.
Here it is in 2012.
A dramatic shot of the place
And a web page about the history of the bunker:
This contest proved considerably easier than we thought it might be. Well done, all hands.
Those who found it (all before the hint) were:
- Eloy Cano
- Paul Voestermans
- Phil Ower
- Luís Filipe Miguel
- steven simmons