Void Pool

For this effect, I started by modeling the ground around the pool, as well as skirt geometry for the edge. I also used Substance designer to create some textures that would be useful for bringing the effect to life. These textures were used for the bright ripples around the pool's edge, the surface distortion, and the falling dust. The falling dust is an additive shader on a grid of quads. A simple particle system below the pool's surface helps sell the impression of a vast empty space.

The object coming in and out of the pool has a custom vertex program that stretches the model out as it gets lower in world space. If I were to implement this in a game, I would base the distortion on the height of the pool rather than set world coordinates and transition the model's shader to a non-distorting one when it's not interacting with a pool.