I'll echo the fact that the fitness room isn't at all crowded on port days, but tends to be a little crowded in the morning on sea days. Earlier is definitely better. There is a locker room, shower and sauna that you can use at no charge. The showers in the rainforest do require that you pay for rainforest use, and they are a real disappointment. The rainforest itself is nice, but the showers are not.
In the locker rooms, they supply towels, shampoo, conditioner, and shower gel as well as hair dryers. Lockers are available on a "space available" basis, as are headphones. You leave your KTTW at the desk to get a locker key or headphones.
Some of the exercise classes get cancelled due to lack of attendance--bummer.
The fitness center supplies water in cups all day. There are towels and spray to wipe down the equipment. The area is small, but generally adequate.