Desert

Sand shows up in a lot of places, but only one stretch of it is the desert that matters. An area flips to desert once roughly fifteen hundred tiles of Sand, Hardened Sand or Sandstone are near you, and at that point the water turns turquoise, the background swaps, and everything picks up a faint heat shimmer. Below that count nothing changes. The enemies do not care about the threshold at all: a single sand block is enough for a Vulture or an Antlion to appear on it, and cacti will grow on it too, which is why a small patch of sand can still ruin an early character. Rain falls here like anywhere else on the surface, and most other biomes take priority over desert where they overlap, including the Ocean.

Every world has one main desert, and that is the one with the Underground Desert under it. Everything else made of sand is a dune: a shallow surface patch, no cave system beneath, occasionally with a small pool of water or a pyramid dropped into it. An oasis is separate again, palm trees ringing a deep pool at the center, and it can generate in any desert in the world. Neither one proves anything about what is below. The clue that does hold up is position. The desert pair always lands on the same side of the world as the jungle, opposite the snow biome and the dungeon.

Half of all worlds give the main desert a visible route into the Underground Desert, in one of four shapes. Chambers are a zigzagging shaft with one or two small rooms hung off the corners. A pit is one wide funnel sunk at the center of the desert. Anthills rise above the sand as cones with a narrow hole punched down the middle, and larva holes are the same idea inverted, funnels dug into the ground with the same narrow drop at their center. The last two generate two or three at a time across the desert surface, so finding one means there are others. The other half of worlds give you nothing and you dig. Celebration Mk 10 and Zenith worlds always put a pyramid at the center of the main desert in place of the normal entrance.

Wind above thirty miles an hour kicks off a sandstorm. Visibility drops, the wind physically shoves you along the ground in whichever direction it is blowing, and a separate set of enemies starts spawning. Early on it is mostly a nuisance, and the shove is worse than it sounds if you are trying to jump a gap. In hardmode it becomes something you wait for on purpose, since a few of the desert's better drops only come from enemies that appear during one.

Corruption, crimson and hallow can all take a desert, and some worlds generate with an infected one already in place rather than waiting for hardmode. The sand becomes ebonsand, crimsand or pearlsand, the music switches to the infecting biome's track, and both rosters spawn at once: the desert's own enemies plus whatever that biome normally sends. Mummies and Sand Sharks are the exception, appearing as biome-specific variants instead of the plain version. Nothing useful is lost. Cacti still drop Cactus whatever color they turn, and Waterleaf still grows in a hallowed desert.

This is the worst biome in the game to put a town in. Five NPCs either dislike or hate it, more than anywhere else, so you pay more and you miss the happiness discounts. Build one or two houses anyway if you want the Desert Pylon, pick residents who can stand it, and keep the real base somewhere else. One more oddity: no boss is tied to this biome, which among surface biomes it shares only with the glowing mushroom fields.