Freefalling on a NASA astronaut trainer plane. ZeroG is a physics lesson about the difference between weight, mass, and momentum. Zero weight, but it still hurts when bumping around. Not to much though. Point being that a 170 pound person may weigh zero pounds in zero gravity, but they still hit...

See a place where divers can swim with stingrays.

Reef Balls are artificial reef modules placed in the ocean to form reef habitat.