The Underworld

Shadow Chests require the Shadow Key to open and contain unique Underworld-only loot.^[1] The Underworld, also called Hell, sits at the world's lowest point.^[1] A vast open cavern runs across the world's bottom, topped by Ash Blocks and floored by big lava pools, Ash Blocks, and Hellstone.^[1] Summoning the Wall of Flesh boss in the Underworld and defeating it switches the world to Hardmode.^[1]

Hellstone, a crafting material found only in the Underworld, burns on contact and gives off half a tile of lava when extracted.^[1] The central half of the Underworld holds several Ruined Houses built from Obsidian Bricks and, more rarely, Hellstone Bricks; these contain Shadow Chests, Hellforges, Pots, Obsidian furniture, and other loot.^[1]

NPC happiness

The Demolitionist, Clothier, and Goblin Tinkerer like the Underworld, while the Mechanic, Party Girl, Pirate, and Golfer dislike it.^[2]

Tips

Wearing an Obsidian Skull or any upgraded version lets a player step on Hellstone and Hellstone Bricks.^[3] A popular way to reach the Underworld fast is by digging a hellevator, a straight vertical tunnel from the surface down.^[3]

Trivia

As a player nears the Underworld, the screen begins to ripple, resembling heat haze.^[4]

References

"The Underworld" (opening section) - Terraria Wiki on wiki.gg, revision 1029888 terraria.wiki.gg
"The Underworld", section "NPC happiness" - Terraria Wiki on wiki.gg, revision 1029888 terraria.wiki.gg
"The Underworld", section "Tips" - Terraria Wiki on wiki.gg, revision 1029888 terraria.wiki.gg
"The Underworld", section "Trivia" - Terraria Wiki on wiki.gg, revision 1029888 terraria.wiki.gg

Text adapted from the Terraria Wiki on wiki.gg (CC BY-NC-SA 4.0), used by Freedom Games LLC, the operator of wiki.gg and Codexery. Page: The Underworld (contributors). Codexery summarised the page: each numbered sentence above was checked against the wiki section it cites before publication, and this entry is shared under the same licence.