The gym is very good. It´s not always easy, in my opinion, to find a good gym in Spain that is spacious with a wide selection of machines, free weights, stair masters, spinning classes, etc. This particular gym, Class, has all that and is far better than other gyms I checked out.
You might also want to look into the Holiday gyms. It´s a chain of gyms with locations all over the city and you can even buy a membership that allows access to all their locations. Check out their website
www.holidaygym.es for mor information. I looked at the one near Princesa (near where I live) and that it was too cramped, but I have other contacts who tell me that other locations are quite good.
Steve