Environments

As of now, the world of Terraria consists of nine officially mentioned environment types.

Forests


Forests can spawn small and large trees, which can be replanted using acorns dropped by chopping down trees. There are many natural caves in forests.

Monsters:
 * Zombie (Night)
 * Demon Eye (Night)
 * Slime (Day)
 * Goblins (Day, during Goblin Invasion)
 * Eye of Cthulhu (Spawnable Boss)
 * Pinky (Day)

Deserts


Large sandy areas that are occasionally generated. Nothing, however, is particularly special about them, as they are completely barren. They have the same monsters as forests.

Underground
The underground consists of two layers: the dirt layer and the stone layer. Ores, pots, and chests can be found throughout. Water is a common sight anywhere underground and demon altars can be found within these layers, however it is a very rare occurrence. Lava becomes common near the bottom of the stone layer. Giant mushrooms have been seen as well.

Monsters: Chests may contain: Pots may contain:
 * Giant Worm
 * Skeleton (stone layer)
 * Mother Slime (stone layer)
 * Bomb
 * Dynamite
 * Flippers
 * Breathing Reed
 * Enchanted Boomerang
 * Hermes Boots
 * Cloud in a Bottle
 * Magic Mirror
 * Band of Regeneration
 * Angel Statue
 * Gold, Silver and Copper Coins
 * Bomb
 * Shuriken
 * Torches
 * Arrows
 * Hooks
 * Silver and Copper Coins

Underground Jungle
The Underground Jungle is a very remote area of the world, residing deep underground. Like Dungeons, these areas have few dead ends; unlike Dungeons, however, they are covered in plants. They have special items that are found in Jungle Shrines, small buildings made of gold blocks that are spawned at random locations in the Underground Jungle.

The Underground Jungle is one of the late game areas and should be avoided by weaker players. Hornets and Man Eaters may 1 or 2 hit a player with insufficient health or armor, and should be avoided until the player has at least Demonite or Meteorite tier weapons and armor.

Underground Jungles are made almost entirely of mud, and this can sometimes reach to the surface, leaving large areas of almost entirely mud at the surface, which can be used to locate the Underground Jungle. Another way to help locate the underground jungle is to dig down to about 700 depth and go laterally. The Underground Jungle is also on the opposite side of the spawn point as that world's dungeon.

They can also be found under or next to corruption. It is located about ~2500 depth.

Monsters:
 * Man Eater
 * Hornet

Jungle Shrines May Contain:
 * Nature's Gift
 * Feral Claws
 * Staff of Regrowth
 * Anklet of the Wind

The Underworld
Main article: The Underworld

A lava-filled, monster-infested hell located below the stone layer. This is, at the moment, the lowest layer in Terraria. It can be considered the most dangerous area, even for end-game players.

Monsters:
 * Bone Serpent
 * Fire Imp

The Corruption
Main article: The Corruption

The Corruption spawns higher-level monsters at all times of the day and should be avoided initially. Corruption is special because it will override nearby dirt blocks to spread, unless the dirt block has a sunflower on it. Chasms, Demon Altars, and Shadow Orbs can be found here. Corrupted areas can be cleared with Purification Powder.

Monsters:
 * Devourer
 * Eater of Souls
 * Eater of Worlds (Spawnable Boss)

Meteorite
After smashing a Shadow Orb, a Meteorite will crash into the planet. It is a small area, but should be avoided by lower-level players. The Meteorite itself is made of Meteorite ore, a high-level material that harms the player on contact (an Obsidian Skull is useful here as it protects from fire-block damage).

Note: It is not suggested that a player build skybridges to get across the map faster if they plan to use that map for harvesting Meteorite ore as it may impact on a bridge and yield minimal resources. A one cube thick bridge will yield 8 to 10 ore in most cases if this happens, considerably less than if it where to impact on the ground.

Monsters:
 * Meteor Head

Dungeons
Dungeons are enourmous buildings found at the edge of a generated world, spanning many layers deep. They're filled with treasure chests and unique items (water candles, books, chain lights, etc.), all of which are spread evenly (chests further down in the dungeons don't necessarily have better loot) throughout the Dungeon. Dungeons are vertical, underground towers, with lots of tunnels branching off the main tower. They are difficult to traverse without grappling hooks or other special items. Dungeons are made of a special brick, the colour of which is determined at world generation. Unique and uncommon enemies spawn in large amounts in this biome. The Skeletron boss must be defeated to enter a dungeon. If you try and enter the dungeon during the day before killing Skeletron he will send his head after you dealing over 9000 damage the player, killing them instantly. During night, if the dungeon is entered, multiple skulls will be sent after you, but the damage they do is similar or identical to Skeletron's spinning head attack.

According to the Production Assistant 'Blue'; there are over 20 different dungeon colours, which are random in each world you create.

Monsters: Chests may contain:
 * Angry Bones
 * Burning Skull
 * Dark Caster
 * Skeletron (Guardian Boss)
 * Aqua Scepter
 * Muramasa
 * Rocket Boots
 * Magic Missile
 * Angel Statue
 * Magic Mirror
 * Handgun
 * Blue Moon
 * Cobalt Shield
 * Band of Regeneration
 * Cloud in a Bottle
 * Hermes Boots

Floating Islands
Floating Islands are masses of land that appear in the sky. Just like in forests, you can find trees and grass growing over dirt blocks, with some stones and ores in the ground. They usually have a building made of ore bricks and a chest inside. In the Alpha version, the quality of the island can easily be identified by the type of brick the building is made of. The bricks show the quality of the treasure inside the chest, while the wall material represents the quality and quantity of the ore that can be found in or around the island. The monsters that spawn here are the same as the ones from the forest.

The islands can be found at different levels of height, based on the size of the map selected.

Note: Use a Depth Meter to find the floating islands,

For small worlds the islands are located around 350 feet.

For normal/medium worlds it is normally around 400 to 500 feet, though can sometimes be found above and below that height. Your best bet for finding one is to go to 430 feet and move horizontally.

For Large worlds they are located between 450-800 feet. It is very difficult to find the islands on large maps because of the various heights, the best option is to get a map viewer that shows where the islands are.

Another way to find floating islands is to craft meteorite bullets and shoot them into the air while traveling. Since metorite bullets richochet, you will be able to tell when there is an island above you, since the bullets will bounce off the islands and fall back down towards you.

Chests may contain:
 * Lucky Horseshoe
 * Rocket Boots (very rare)
 * Shiny Red Balloon
 * Starfury