Submitted by Miles, who says:

When I was at Miniatur Wunderland in Hamburg (the largest model railway in the world), I found a tiny rendition of the Hamburg subway map in one of the models. It was  a very detailed map, although my photo is blurry because it was so close up.

Transit Maps says:

Looks just like the real thing! It’s probably a tie between this map and this generic one for smallest subway map I’ve seen yet. Unless someone’s etched a Tube Map on a grain of rice with a laser just because they could?