Magma Fields

The Magma Fields are a randomly-generated location in the Crystal Hollows where Yogs can spawn. When in the Magma Fields, the player's gradually rises until they begin to burn and take damage.

Lava in the Magma Fields bypasses the Lava and Fire Talisman effects, but not the Campfire Badge effects.

The Magma Fields provide a bottom entrance to the Crystal Nucleus and can house Khazad-dûm.

In addition, it is possible to fish in the lava within the Magma Fields, with a separate loot table to normal fishing.

Trivia

 * Early on in the release of the Crystal Hollows (0.12), lava Fishing in the Magma Fields had vanilla Minecraft loot tables, leading to lots of glitched items.