Great workout facility. I used it when we were there 2 mths ago. It's a nice sized facility with plenty of cardio equipment. There were approximately 6 of each types' of cardio equipment so even when it got busy (which it never was too busy and this was on the weekend in the morning around 9ish)...but there was never a wait for any of the equipment.
They also have a nice assortment of nautilus/universal equipment and an area with free weights. There are also towels and a water cooler.
It's located in the main bldg. I actually entered (not knowing) through the back way which is in the courtyard area by the arcade and across from the activities center and took the elevator to the 2nd floor and it was right there. Otherwise just look for the SPA and you'll find it (by the main pool area).
I do have to add, if you're going during a cooler time of year and like to do the treadmill, the grounds at SSR are great to run/walk around. You can easily do several miles and even cut over through DTD and in the mornings it's not open so you don't have to worry about dodging people.

I actually walked around SSR for a few miles and then ended up at the fitness center to finish my workout.
There is no charge if you're
DVC or if you are staying at SSR. We'll be back there in 2 weeks, hoping to use the fitness center again if I can.