CaveMC is a semi anarchy survival server that feels like vanilla but harder. The whole overworld is underground so there is no surface at all. It is all caves with biomes resources and structures packed into one giant cave world.
Season 2 is out so it is a fresh start with a bunch of additions. Survival is brutal and you have to be smart to last.
There is also a Wasteland Dimension coming on November 8th. It adds new gear huge mega structures and secrets to find. It also has its own currency so players can trade and build a new economy. There is a new spawn too and the map is custom generated with special features.
