The Shimmering Frontier
The Shimmering Frontier is a full ring around the outer biomes with smaller sections of it embedded within the outer biomes as you get closer to it.
It's a bright, blue, crystal-based biome made from 
Crystal Block and shimmering water. It's the source of 
Solarite Ore, 
Gleam Wood, Upgrade Gems, 
Sunrice Seed, 
Lunacorn Seed, unique Critters, and unique fish.
