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There was a bomb disposal facility I stumbled upon in the middle of Grunewald, Berlin. Me and my friend were wondering what the fencing/building was, when we heard a siren go off. Ten seconds later, we heard a loud BOOM, and got out of there ASAP. Didn't take any pictures, though.
I just now did a bit of research, and apprently it is known as "Sprengplatz Grunewald". It doesn't look so impressive from the pics I could find on the net, but it was nonetheless unexpected and creepy.