[rsynnott]

A while back I was in Berlin, and got lost in Nollendorfplatz station (which is not particularly _big_) for about ten minutes. Now, for various reasons I had been awake for about 36 hours, so mostly blamed it on that, but if this site is correct it confirms my suspicion that that is a weird station. U1 and U3 are on different levels for different directions!

[lansol]

Maybe not common, but not an uncommon design. It is so you can transfer between lines by crossing the platform.

https://en.wikipedia.org/wiki/Cross-platform_interchange https://www.youtube.com/watch?v=E5hXH_mLPzw