I really like the Sapporo underground train system. Sapporo's not actually that big, so it never takes long to get anywhere; the trains (as they are everywhere in Japan) are very clean; the carriages (as you can see here) are exceptionally spacious, and there are no doors between them! This means that you can sit at one end and just watch the train weave and bend as it makes its way through the tunnels. They run on rubber tyres too, rather than rails, which means that they're quiet on the approach (but they're pretty loud when you're on them if the windows are open).
Anyway, I took this picture a couple of weeks ago and forgot to upload it. Feast yer eyes baby.