Region of reverse gravity: while inside the region you gain levitation if you don’t have it, or lose levitation if you do have it. This means if you want to pick something up off the floor, you would quaff a potion of levitation. If implemented as a separate effect on top of levitation, you might have no control over your movements, as you do on the Plane of Air - magical sources of levitation give you control over your movements there, but in order to be levitating in a reversed-gravity area you cannot have any levitation magic.

Not specified what effect would create the region.