The gym is set up so that the ground floor (American first floor) and first floor (American 2nd…read morefloor) both have weight and cardio machines, as well as some free weights. There's a small winding staircase to the second floor (American 3rd floor) that has the women's and men's locker rooms, which also have showers. There are no WCs or sinks in the locker rooms, only showers, which can be kind of a hassle, but there are toilets on each of the other floors of the gym.
Pros:
--open on Sundays and holidays (8:00-18:00)
--location
--new equipment
--lots of cardio machines with video screens and iPod plug-ins for watching TV and movies (cable or from your iPod)
--women's locker room has plastic bags for wet/dirty things, hair dryers, spray deodorant, and body lotion; and often also hair ties, hair spray, Q-tips, cotton pads, and other odds-and-ends for getting dressed and putting on make-up after a work out and/or shower
--the showers seem pretty new and clean
--they'll make you a "personal offer" for gym membership (monthly price) based on how often you're likely to go to the gym per week, etc
--free trial day
--free work out plan with a trainer (set goals, learn how to use the machines if you don't already know, etc)
--there are always several people working there, and there's a "bar" with protein shakes and sports drinks, as well as bottled water and fruit for sale, etc.
Cons:
--opens relatively late every morning (8:00-22:00 M-F)
--no air conditioning
--limited number of free weights
--no classes
--no WC (or at least lavatory) in locker room
--located on Mariahilfer Straße, so kind of a pain (although easy to get to by the U-3 U-Bahn at the Neubaugasse stop)
--no monthly contract available - yearly only
--gets really busy at rush hour, starting around 16:30, and is super busy by 18:00
--very minor con: that creepy logo with the caricature of the owners/managers (?) is everywhere in the gym (it's on their website if you want a closer look - my pictures don't show it very well).
A pro & a con:
ISC provides lockers with built-in locks (so you don't have to bring your own lock), and you get the key when you arrive/check-in with the locker number on it (and it's on a chain you can wear around your neck while you work out - see the picture). However, you can't choose which locker you want and, for me at least, some are located in better places than others (particularly in the women's locker room), such that I'd rather just bring my own lock and have my pick of the lockers.
They do have smaller lockers available for rent (only €25/year!), but there's a pretty long waiting list to get one of those.