The newest (as of September 2003) attraction at Epcot
undergo "flight training
" at the International Space Training Center
, for an eventual mission to Mars
The ride is effectively four centrifuges, with ten pods mounted to each. Four people ride in each pod. With the centrifuge, the ride can generate a simulated gravity of up to two Gs. This is used repeatedly during the ride, to simulate liftoff, lunar orbit insertion, and descent to the surface of Mars.
I don't recommend riding if you're prone to motion sickness. This ride has a nickname of Mission: Spew, and it can certainly live up to its reputation. If you have a stomach of iron, though, it's really a thrilling ride.
(An additional note: Although the ride is themed after the movie Mission to Mars, it is infinitely better.)