Is this not one of the coolest subway stations you've ever seen or what?! The architect of this station, Zbigniew Peter Pininski, certainly did a good job of standing out from other stations with his breakout design.
Frankfurt was quite quiet on the Sunday morning that I was there. The whole subway system was interesting to me. It runs on the honor system. You must buy a ticket, but there's no turnstiles or gate to go through. Apparently there are supposed to be plain-clothes ticket inspectors to check that you have a ticket. I bought a day pass, and rode the train all over town, but no one ever asked to see my ticket.
Entrance to Bockenheimer Warte Subway Station