Here's what you get if you don't pay for a gym membership:
Track access, squash courts, and basically any facility usage except for the Pulse.
If you buy a gym membership:
Access to the Pulse, as well as the climbing wall, as well as free admission to the classes within the Pulse.
What you don't get with a gym membership and you still have to pay for regardless:
Intramurals of any kind, or the classes outside The Pulse like Kickboxing, Aerobics, Yoga, etc.
Hope that helps
