I was on my way to a "Fourth Advent" party at a friend's place a couple of weeks ago when I spotted what I thought could be a Banksy on a wall of the old jailhouse. I tried to find out if it is a Banksy or not on the internet, but have so far been unsuccessful. Maybe someone out there can confirm one way or the other.
To the right of the possible Banksy, the lower wall has been wallpapered over with some interesting glued on figures reminiscent of Banksy. I think it's pretty damn cool and is something to see if you're ever in Frankfurt. You can check out the location on Google Maps with Street View here, when the wall was blank. The address is Klapperfeldstraße 5.