For those of you planning a longer stay in WAW, I strongly recommend the Sheraton Warsaw Fitness Centre.
I actually live nearby and I've been using their gym and sauna facilities for over 6 years now.
The quality of the equipment, cleanliness of the facilities and lack of crowds are its main advantages.
There are two saunas: steam room and dry sauna - separate in men and womens changing rooms.
There is no swimming pool but usually at hotels the pool is small and it only raises the price.
Also highly recomended are the fitness classes, out of which I personally attend just one: Precision cycling - a good way to burn extra calories during a1 hour training session.
Equipment: usually gym wear recommended: towels are provided as well as the shower gel,
the standard of a 4 star hotel is also maintained downstairs - i.e. at the gym
the workout equipemnt ( treadmills, cross trainers, etc) was replaced with the new one two yrs ago
Should you be staying in Warsaw for longer and wish to subscribe to a fitness center, I'd recommend anything but World Fitness.
World Fitness offers poor service, dirty lockers and slimy showers at high prices. The main attraction is that they do not obey their contractual duties.