Colditz

The building in the bottom left-hand corner is Colditz Castle. Or it is if you are 9 and growing up in the 1970's. Your mission is to approach the castle without being spotted by the snipers in the tower. (Why anyone would be trying to get into Colditz Castle, rather than escaping from it, is as yet unexplained.)

If you are a boring grown-up, it's a Brewing Industry Research Foundation building (which sounds as though it could be quite fun in a different way).