Frankfurt has an amazing amount of hookers and walkups near the station. can be quite rough, as it has a large population of drug addicts/junkies and local criminals around the station - especially weekends and in the evenings, but due to the large numbers of hookers, you will always find something reasonable.
Hannover is probably one of the lesser known places - and my preferred place for walkups in Germany! Decent prices, large selections of walkups and there are a few stunners others than your 101 Romanian/Bulgarians. Its a nice city as well and very easy to get to from London.
Places to avoid are Cologne (two large walkups and a few small ones) but its expensive and loads of people you want to avoid. The two large walkups are basically just outside central Cologne located between a motorway and a park. a bit dodgy. Hamburg is fun but need to be careful as a rip-off and loads of drunken tourists. Places like Dusseldorf are just shit. Never seen something like this before but there is a 7 story building and the girls sitting by the window. Every window has a number and you look around, if you think you like a girl (if you can tell from the distance, i cant because of my bad eyesight) you remember the number, walkup and knock on the door - then you are in for a surprise or you trust your eyes. bring your binoculars! Dortmund - too small and horrendous city.
munich, really cool city, few small walkups. can be fun during summer time. Aachen has a good reputation but havent been there. Bochum has actually quite a nice little red light district with a few walkups - but just difficult to get there from London.
