Ruined Houses are structures in The Underworld, generated at world creation. They appear as towers built from Obsidian Bricks (with Obsidian Brick Walls) or Hellstone Bricks (with Hellstone Brick Walls) with several rooms each, causing them to somewhat resemble apartment buildings. They are often partially (sometimes completely) flooded with lava. Ruined Houses occur frequently, but only in the middle 50% of the Underworld; there are no Ruined Houses at the final 25% left and right of the Underworld.
Ruined Houses commonly contain several Pots, Hellforges, Demon Torches, Obsidian furniture items, paintings, and decorative banners. They also often contain locked Shadow Chests (nearly all Shadow Chests are found within or on top of Ruined Houses). Hellstone is commonly found among the Ash Blocks beside Ruined Houses.
- The furniture found in Ruined Houses, with the exception of Demon Torches, is not dislodged by contact with lava, unlike most other furniture. These items can still be destroyed by throwing them into lava in item form.
- Due to the fact that Hellstone Bricks cause the Burning debuff, Ruined Houses made of Hellstone Bricks are much harder to navigate without taking damage until an Obsidian Skull is obtained. There is no other significant difference between the Hellstone Brick and Obsidian Brick variants.
- As the furniture found in Ruined Houses is not destroyed when in contact with lava, the Obsidian Brick that makes up most Ruined Houses can be harvested and subsequently crafted into platforms, which can be used to make a bridge across the Underworld that will not be accidentally damaged or destroyed by lava.
- Despite the name, Ruined Houses do not look particularly ruined – the name is a remnant from older versions of Terraria in which Ruined Houses had random holes in the walls and background walls. Current Ruined Houses will still occasionally feature lacking horizontal walls, but these holes are more strategically placed to allow entry into rooms. The holes are furthermore harder to notice with the background walls lining up. There is also the occasional half-block creating lavafalls.
- Desktop 1.2.4: Added Obsidian Clock, Obsidian Candelabra, Obsidian Lantern, Obsidian Chandelier, Obsidian Dresser, Obsidian Lamp, Obsidian Sofa, Obsidian Bathtub, Obsidian Piano, and Obsidian Candle.
- Desktop 1.2:
- Wood Platforms replaced by Obsidian Platforms.
- Added Obsidian Chair, Obsidian Table, Obsidian Work Bench, Obsidian Bed, Obsidian Bookcase, Obsidian Vase, Paintings, Banners, and other decorative items.
- Changed generation; there are no longer holes in the background, and rooms can be generated horizontally.
- Desktop 1.0.6: Now spawn differently. They often spawn as all Obsidian Brick, and they can now be very tall.
- Desktop-Release: Introduced.
- Console-Release: Introduced.
- Switch 1.0.711.6: Introduced.
- Mobile-Release: Introduced.
- 3DS-Release: Introduced.