Cavern

The Cavern Layer is under the Underground Layer. It begins at about -850ft below the Underground. Mother Slimes, Black Slimes, Giant Worms, and Skeletons spawn in this area. The Cavern Layer is usually rich in mineral deposits, the lower one travels the larger gem veins will become on average. Also it should be noted that Lava begins to appear around -2100ft in small pools, which gradually become lava wells at around the -3000ft mark.