Aether

The Aether is a Pre-Hardmode mini-biome that contains a cave made of Stone Block, a large pool of Shimmer in the center,  and Gem Trees. It also has a unique feature that causes all fully dark blocks to appear as a background with stars, resembling the background of Space.

Location
The Aether is located underground on the Jungle side's outer fifth of the world. It is most commonly found in the general area under the beach at the shoreline of the Ocean, but can be found far enough inland to be within the Jungle.

Vertically, it can be found in the Underground/Cavern layer anywhere from 100 to 2200 blocks down depending on the world size. It's most commonly found a little bit above the layer where lava begins to appear.

Tips
It is recommended to construct a bridge made of Platforms over the pool of shimmer to make going from one side of the cave to the other easier, as well as prevent most Enemies from falling in and becoming invisible. This will cause Item Transmutation to be less convenient, so you should also make a small hole in the bridge.

Trivia

 * Faelings can spawn even if the Journey Mode spawn rate is set to 0.