- See also: Desert.
The Underground Desert is a biome located directly underneath a Desert Biome. The entrance can be found on the surface in the form of a deep funnel shape, opening into the biome at the bottom. The entrance is always within one of the Desert biomes created upon world generation. Each world will have only one Underground Desert, despite potentially having multiple Deserts.
The Underground Desert is made primarily of tunnels of Sandstone Blocks. It can also have Underground Cabins made of its biome-specific materials. It is very large when fully explored, rivaling even the dungeon in size. It always has either a circular or oval shape. The Underground Desert is home to several species of Antlion, among other enemies.
In Hardmode, the Underground Desert becomes significantly more challenging. Along with harder enemies, the Underground Desert is extremely vulnerable to conversion by Corruption, Crimson, or Hallow, due to the biome being made of Hardened Sand and Sandstone, both of which being susceptible to conversion. Conversion further strengthens the Underground Desert's enemies, and in Corruption and Crimson Underground Deserts, causes the spawn of Desert Spirits.
- While artificial Underground Deserts can be created by placing their respective blocks, no unique enemies will ever spawn due to lack of specialized back walls. It shares this trait with the Dungeon.
- It seems that the Underground Desert has more Iron or Lead Ore than other ores.
- The enemies are very dangerous early on, so it is advised to have ample Grenades on hand as well as some form of movement-based Accessory to make it less difficult to deal with them. Gold/Platinum armor is recommended due to the high damage dealt by the Antlion Swarmers and Chargers.
- In the real world, larval antlions create funnel-like pits in the ground and fling sand at prey that pass by. The entrance to this biome may be based on this behavior.
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