Sauna Babylonia is very famous and has been around for a very long time. It's very conveniently located in the centre of the city in a little side street.
The sauna is located on two floors and the wet area seems to have been renovated very recently. The steam room is very nice and big, with lots of corners, seating, etc....
The cabin area can be found downstairs and has about 8 cabins plus a big video room area.
One of the guest said that their foam party is very popular.
The newer big Prague gay sauna is called Sauna Labyrinth and is a little bit outside of the tourist area, but not that far with the metro.
It is definitely bigger then sauna Babylonia, altough in style it feels a little bit more dated.
I liked their steam room which really was a well thought out labyrinth. Otherwise, all wet things are provided.
An extensive cabin area as well as glory hole cabins provide plenty of space for cruising.
If you are going to visit, check out both.