Lava Lakes

The Active Lava Zone is an in-development biome. It is presumably where the Sea Emperor is being held. A precursor Seabase will be present in this biome. 

The Active Lava  Zone will be smaller than the Inactive Lava Zone.

Lava lakes and lava falls are a common sight in this biome, along with obsidian pillars, and rock formations.

Sea Emperor Prison
The Sea Emperor Prison is an in-development location within the '''Active Lava Zone. '''It is hinted that the Sea Emperor will be imprisoned in this area.