The Underground Desert is a biome located directly underneath a Desert biome. The Desert above may generate different features which informs that the Underground Desert is underneath (see Surface Desert below for details). The Desert/Underground Desert pair will always generate on the same side of the world the Jungle is on.
The structure of the Underground Desert resembles that of a real-world ant hive, featuring numerous small caves mainly composed of Sandstone Blocks and Hardened Sand Blocks, which are connected in varying degrees. It is very large when fully explored, rivaling even the Dungeon in size, and is always either circular or oval in shape. The Underground Desert is inhabited by many types of Antlion enemies and is also riddled with traps, making it a challenge to navigate.
The Underground Desert becomes significantly more challenging in Hardmode. Along with harder enemies, the Underground Desert is extremely vulnerable to conversion by Corruption, Crimson, or Hallow due to Sand, Hardened Sand, and Sandstone all 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.
The Desert above the Underground Desert may generate with various surface features, including one or more Oasis mini-biomes, or one of several types of the entrance. There is a
33.33*1/3 (33.33%) chance that a world's main Desert will contain one of the various types of the entrance. These can assist in locating and accessing the Underground Desert from the surface. The presence of an Oasis does not indicate where the Underground Desert is, as the Oasis mini biomes can generate atop any of the world's Deserts, regardless of which of them contains the Underground Desert biome.
It is possible for one or more Pyramids to generate in the main Desert. When this happens, the Pyramid will often extend somewhat into the Underground Desert, and thus its tunnel can provide another easy means of entry. As with the Oasis mini-biome, Pyramids can generate in any of the world's Deserts, regardless of where the Underground Desert is located, and so their presence does not guarantee that the Underground Desert is below.
See Desert for more information about the surface entrances to the Underground Desert.
- 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.
- While it is possible to craft Sandstone Walls and Hardened Sand Walls via the use of Ecto Mist, these walls are considered "safe" and will prevent enemy spawns.
- The border between the Underground Desert and the Cavern layer often feature pools of lava much closer to the surface than where lava would normally generate.
None of the Underground Desert enemies require an actual Desert biome to spawn. The three "tainted" Ghouls each only spawn in their respective Corrupt/Crimson/Hallowed biomes. When in an evil biome, dark-haired Lamia will replace their counterpart and Desert Spirits will replace Sand Poachers. Antlion Larvae only spawn when Antlion Eggs are broken.
To successfully spawn an enemy on a selected tile, the following checks are done:
- The spawn tile must be more than 10 tiles in from any edge of the world, including unreachable tiles.
- The spawn tile must be below the halfway point between the Surface and the top of the world, including the unreachable tiles.
- The spawn tile can be any active (not actuated) solid block, which includes platforms or any other valid spawning surface.
- The wall behind the spawn point and the 49 tiles above it must each be either Sandstone Wall (or its "tainted" variants) or Hardened Sand Wall (or its "tainted" variants)
- 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.
- Minions give several advantages in the underground desert that most other weapons do not. The underground desert's main dangers are fast-moving, knockback resistant enemies and rolling cacti. Minions counteract these by being summonable on the other side of walls, reacting to quick-moving enemies without requiring player interactions, contributing knockback independently of the player's actions, and triggering rolling cacti remotely (which may require summoning them directly on the cacti multiple times or waiting to summon them until an enemy passes by).
- In the real world, larval antlions creates funnel-like pits in the ground and fling sand at prey that pass by. The funnel and burrow entrance types to the Underground Desert are presumably inspired by this.
- Prior to 188.8.131.52, the Desert above the Underground Desert would always contain a large Pit-style entrance. This made it easier to find and access the Underground Desert.
- Desktop 1.4.4: Increased the minimum size of Underground Deserts from 50% of the maximum size to 75% of the maximum. The maximum size has not increased.
- Desktop 184.108.40.206:
- Added Sandstone Chests in world generation.
- Generation changed to make the biome go to varying depths, making it much deeper than in previous versions.
- Introduced a brand-new music track for the Underground Desert.
- Lava now spawns at lower levels towards the edge of the biome.
- The Desert above the Underground Desert may now generate other features than the funnel entrance, and the funnel design has also changed.
- Desktop 1.3.3: Increased spawn rates.
- Desktop 220.127.116.11: Introduced.
- Console 1.0.933.1: Introduced. ()
- Console 1.0.750.0: Introduced. ()
- Switch 1.0.711.6: Introduced.
- Mobile 18.104.22.168: Introduced.