More underground structures and Deep sea abyss

The underground could use more structures, nothing fancy, but with the new huge caves, there is a lot of potential for underground ruins that have chests with underground loot like diamonds and amethysts. I've seen many posts about a Deep sea abyss. This biome would be so dark unless you had glow ink on your armor or a new throwable light source. Glow squid and Angler fish could spawn down here as well as some really good loot you can find. The ground would be speckled with runes and loot and some new miniboss like the leviathan from Subnautica who would come out of nowhere and the only way to find out if it is coming or not is to listen for its screech. It would add that same sense of terror to the game that you got your first time entering a dark cave and seeing a zombie come out of nowhere. Of course, a leviathan doesn't have to be the mob but something big that is almost unkillable like the new warden would make it terrifying and dangerous to explore the abyss (the deep dark of the ocean). These are all ideas and could be changed around but the main idea is here.