Aether

The Aether is a mini-biome that contains a large pool of Shimmer. It also has a unique feature which causes all fully dark blocks to appear as a background with stars, resembling the background of Space. The Aether is located underground on the Jungle side's outer fifth of the world, usually below the Ocean. It can be found in the Cavern layer anywhere from 100 to 2000 blocks down depending on the world size. It's most commonly found where lava begins to appear.

Contents
A natural Aether consists of a large pool of Shimmer in the center, surrounded by stone and Gem Trees. An artificial Aether only needs the Shimmer, but at least 300 blocks of it. The only naturally spawning mob is the Faeling, but the Shimmer Slime can also be created through the use of Shimmer. These are the only two mobs exclusive to the Aether and it's contents.