Clapham Common tube station (opened 1900) is one of only two remaining tube stations with a narrow (3.6m) island platform. It serves both northbound and southbound lines, which is useful if you change your mind about which direction you wish to travel in mid-journey or if you're playing the accordion up and down the northern line looking for tips (for example: "the central line carries richer passengers").
Before I moved to London I was really anti London-centric stuff, but now I won't go anywhere without an underground rail system and a teenage stabbing a week.
I like this kind of faux-silk-screened look. The colours look like they only took five minutes, but don't be mistaken (they took two).