The Underworld

2013-10-15 00001 — Typical Underworld scenery with Classic background

Terraria Underworld Background — Current Underworld background

The Underworld, also known as Hell, is the bottom-most Biome in the game, reached by digging past the Stone Layer. The Underworld can easily be differentiated from other biomes due to the background wall changing to a hellish semi-flat landscape with lava ponds and large pillars. Prior to 1.3.0.1, it was a veiny lava-rock wall.

The Underworld contains mostly intact buildings called Underworld Houses, which may contain Pots, Hellforges, and any kind of Chests. Prior to 1.2, these houses were frequently very damaged or partially complete. The Underworld is the only biome where Hellstone, Ash Blocks, Hellforges, Fireblossoms, Shadow Chests, and others may be found. Healing Potions can be found in pots instead of the Lesser Healing Potions that tend to be found in other areas. Additionally, it contains stronger enemies than most other pre-Hard Mode biomes.

The Underworld begins at around 1000-1500 on small worlds, 3000-3200 feet on medium-sized worlds and around 5000 feet on large worlds, but it may start at around 2000-2500 feet in medium worlds in some instances.

Monsters[]

Mob	Abilities	Health
Bone Serpent	Able to travel through lava and all blocks, has properties similar to The Destroyer.	250
Demon	Fires Demon Scythes at a player. Low chance to drop Demon Scythe.	120
Fire Imp	Can shoot Fireballs through blocks at a player, which can be blocked with any attack.	70
Hellbat	A Underworld version of the Cave Bat.	46
Lava Slime	Behaves as a a regular slime, but it can swim in lava without being harmed.	50
Voodoo Demon	Just like a regular Demon. Always drops the Guide Voodoo Doll when killed, which will summon the Wall of Flesh if it falls or is dropped into Lava.	140
Red Devil (Hardmode)	Similar to the Demon, but fires much more powerful tridents, and it also has more health.	600
Lava Bat (Hardmode)	An upgraded version of the Hellbat, but is slightly more powerful and has more health than the Hellbat.	160
Arch Demon (Old Gen And 3DS only)	Essentially the same as a standard Demon, but shoots more Demon Scythe projectiles at a time, spawns less frequently, and does not drop the Demon Scythe spell.	120
Wall of Flesh	This is a summonable boss (Toss a Guide Voodoo Doll into lava to summon). See Wall of Flesh article for details.	8000 /11200 (Expert)

Reaching the Underworld[]

My Hellevator... — An example of a Hellevator

Early game, you will find that as you explore caves deeper and deeper, you will eventually hit The Underworld. This, however, is not very effective as if you wish to frequently revisit The Underworld; it may take 5-10 minutes traversing the caves to reach the Underworld.

Once you have the time and resources, it is well worth the time to make a Hellevator. This is essentially a 2 block wide hole that goes all the way down to The Underworld, allowing you to jump in and wait as you fall all the way down.

Note: If you don't have a fall damage negating item such as Wings or a Lucky Horseshoe, make sure to place a few blocks of water at the bottom so as that you don't take any fall damage. However, you should be sure to end it right before the Underworld, since water in the Underworld evaporates.

While it is debatable whether it is worth the time and money, a Teleporter from your house to The Underworld is by far the fastest way to get down there. However, depending on the world size, this can cost several platinum coins.

Recommended Items[]

There are several items that are highly recommended to bring whenever you visit The Underworld.

Cloud in a Bottle/Balloon (or other double-jumping items) and/or Rocket/Spectre Boots
The Underworld is filled with large pockets of lava that can be difficult to get over without the assistance of a double jump and or boost.
Grappling Hook
Very useful for a quick save, to avoid taking a dip in the lava pools, as well as getting you out of them as quickly as possible. It's also useful for getting over those large pockets of lava mentioned earlier.
Obsidian Skull/Horseshoe/Shield
These especially useful while mining Hellstone as they will protect you from the constant fire damage from the blocks. Since the surface of The Underworld is lined with Hellstone the Obsidian skull's ability to negate damage done while touching Hellstone is very useful.
Lava Waders
As of 1.2, the Lava Waders are one of the best accessories to bring to the underworld. Not only do they allow the player to walk on the surface of lava unharmed, they also allow the player to take brief dips (up to 7 seconds) into lava without harm.

Mining[]

The only ore available in the Underworld is Hellstone, which is used to create Molten Armor and other molten items, which is the highest tier of armor and tools available before activating Hard Mode. Upon contact with Hellstone ore, the player will receive fire damage, which can only be prevented by equipping an Obsidian accessory, like the Obsidian Skull, Obsidian Horseshoe, Obsidian Shield, Obsidian Water Walking Boots (the latter three are created by tinkering the original items with the Obsidian Skull at a Tinkerer's Workshop), and drinking the Obsidian Skin Potion.

The most important thing to note is that mining Hellstone will spawn approximately half a tile of lava for every block mined out. As such, it is advisable to always keep at least a one-block-thick wall of blocks between oneself and the ore being mined. Ash Blocks are found abundantly throughout the Underworld and will serve very well for this purpose. If attempting to mine around smaller lava pockets, it is best to dig out additional sections in order to cause the lava to flow elsewhere, out of the way, rather than attempting to tunnel through it in any fashion.

Always keep at least a one-block-thick wall between oneself and any lava pockets or ore deposits being mined to avoid being surprised by a sudden lava flow, and ending up dead.

Notes[]

Placing 50 Meteorite will stop underworld monsters from spawning, and replace them with Meteor Heads.
It's highly recommended for players to take Obsidian Skin Potions or Water Walking Potions to avoid lava damage. If you can't find them or anything that works in a similar fashion, at least obtain Rocket Boots and any Grappling Hook.
The very bottom of the Underworld has an invisible boundary like the far left, right and very top of the map. Touching this invisible barrier will give the "Rock Bottom" achievement. You can use the Obsidian Skin Potion to easily do so as it grants 3 minutes of lava immunity which is more than enough.
Fireblossom, Daybloom, Waterleaf, and Blinkroot can grow in The Underworld. It may be possible for Moonglow and Deathweed to grow as well.
The Underworld is the only biome where Hellfire Arrows and Shadow Chests (a rare chest that contains rare items) may be found.
When you start traveling along the Underworld, leaving the area with the houses and closer to the edges, the spawn rate of monsters gets noticeably higher. This is because the majority of the monsters spawn either in lava (Slimes) or in empty space (Demons and Hellbats).
The amount of Lava in the Underworld isn't infinite, so it's theoretically possible to remove all the lava down there by turning it into Obsidian if you've got sufficient supply of Water. Bottomless Water Bucket theoretically works.
Any water left stagnant in pools will evaporate in the Underworld, and although a glitch makes it possible to have pools, removing blocks around the water will cause it to evaporate.
Heart Crystals are far easier to find in The Underworld than in other Environments.
It's possible to encounter Underworld Monsters from the Cave layer or from the Underground Jungle.
You can find it easier with a Depth Meter or GPS.
In the Console Version, Hellforges will spawn in the lowest areas of The Underground rather than in the Underworld itself. (Fixed, they now spawn in the correct place.)
Previously, the Underworld ironically became easier than the other biomes in Hardmode due to the lack of new monsters in Hardmode. As of 1.3, there is the Red Devil which is relatively common and also highly dangerous. Additionally, the Corruption/Crimson and Hallow both intersect in the Underworld after the Wall of Flesh is destroyed, so you can farm for souls there.

Trivia[]

The new background and music in v1.3.0.1 do not remove the original 2 backgrounds. According to looking at it, it might have pushed up to the lower cavern. This does not count the area where lava starts. So you should be lucky it's still there but higher.