A very special place exist in Russia in "Zvezdniy gorodok" (Star City) near Moscow - Space Hydrolab: Neutral Buoyancy Training Module for Space teams. Full set of training modules of International Space Station is submerged in a huge swimming pool ready for cosmonaut's training.
On workdays a real cosmonauts train hear, but on weekends everyone can dive here. Only 2 places like that exist in the world: Zvezdniy gorodok and Houston. If you happen to be in Moscow, you could also arrange your diving here. The link to hydrolab dive-center web-site is: http://www.space-dive.ru/
(sorry, it's in Russian).
Hydrolab pool is very large - about 30 meters (100 feet) in diameter, and 10 meters (30 feet) deep. But ISS is bigger than that, so the hydrolab crew can arrange what the parts of the station are submerged. To change the parts they are put on top of large platform that is suspended on 4 huge chains.
The water is warm (28С / 82F) and very clear. The most part of modules is empty inside, 'couse the training actually happening outside. The astronaut train here in real space suits, with additional weights added to archieve neutral bouyancy. Space suite is very heavy, so they put them on lifting rope.