Underground Crimson
They improve your capabilities
It looks like purgatory\limbo... not the bottom of the sea(
castiron steel Damascus
Underground desert
Underground ice desert
Vegetation in the Dark sea has a red-orange color.
Icy desert landscapes
Animals from Crimson biom
In the screenshot you can see: Shale, Ash, Magma stone.
High tech aquamarine valley
in 1.17 Added a number of things for travelers (ropes, diving suit, Glowstick) and Hunters (skins, strange meat and cooked rotten flesh)
It will allow you to study underwater biomes more comfortably
One of the structures