Underground

The New York subway system is functional and mostly clean, which is really all that I can say about it. The Washington DC metro is elegantly designed, if showing its age, and mostly clean.  The Boston metro has always fascinated me because of a) the trolleys that are part of it, and b) the Park Street Green Line Station with its elegant lights (last time I saw it, which, granted, was about 20 years ago).

But the Stockholm metro.... I wouldn't go there just to see the metro, but if I was in the area....