Cavern

The Cavern layer is below the Underground layer. It begins at about -850ft and can be noticed by the darker stone backdrop wall. Stone largely replaces dirt in this layer. Mother Slimes, Black Slimes, Giant Worms, Bats, and Skeletons spawn in this area. The Cavern layer is often 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. You should however note that these measurements are different on different world sizes. Blinkroots can be found here. One must be extra cautious at the lowest levels of the layer at the border between Cavern and Underworld because Underworld enemies can ambush unsuspecting players.