I went indoor skydiving at iFly
yesterday, as part of a friend's bachelorette party. The great thing about indoor skydiving is that it eliminates the scariest part of skydiving: jumping out of an airplane that is very high up in the sky. With indoor skydiving, they basically stick a huge fan underneath a mesh floor and blow air at you at very high speed. You hover a few feet above the floor. No heights, no falling, no potential for going splat.
In terms of what it feels like, it's similar to scuba diving in terms of the sensation of weightlessness, but you're in a very rapidly moving medium, and so very small changes in the position of your arms and legs can change your buoyancy or stability. So you tend to find yourself shooting up and down in the wind tunnel, or bouncing from side to side. (They have an instructor in the tunnel with you, to keep you from going totally out of control.) By my second flight, I was starting to experiment with how changing the position of my arms would change my vertical position in the wind tunnel, but I think I'd need a lot more practice to really be able to control my flight.
Anyway, I recommend the experience highly!