in Bonn are around 10 Gyms. Most of them where more "Fitness". The old "Health Center" (Eifelstraße), which is not far from the center of Bonn, is a good option "for serious training". There is also a Bus- and a Subwaystation only a one minute Footwalk away. You can also pay "per Day". Last price i know is 5 euro/day. The gym is open from Mo.-Sunday (M.-Fr. up to 10 PM, on Saturday up to 6 or 8 pm ?, on sunday it`s open a few hours. The gym equipment it`s not new but ok. They also have a webiste in the internet. If i can find the link i will post it here. I train sometimes in Bonn, but living 20 Minutes outside of Bonn.