there are lots of mysterious door and buildings in london (as any city). here is one with a door which is extremely well secured shut.
a few minutes before seeing this building, in another part of London, i saw a street paving stone has been lifted up and there was a very long and deep staircase down under the road. i was going to take a photo only there were two security chaps inspecting me inspecting their hole.
i find that kind of thing fascinating.