Treasure rooms are spawned with world creation and appear to be man-made structures. They always contain some form of treasure and sometimes have light sources, furniture, and other decorations. Unless otherwise noted the walls, contents and backgrounds of these rooms can be harvested. Treasure rooms include:
Underground cabins are typically wooden buildings full of dusty, broken furniture as well as chests, vases, and occasionally usable furniture and decorations. They are found in the underground in the cavern and snow biomes.
Ruined houses are generated at World creation in The Underworld in the middle third of the Underworld (laterally). They are towers with multiple levels, constructed with missing parts for a "ruined" look, from Obsidian Brick or Hellstone Brick. They are sometimes partially submerged in lava and often contain deposits of hellstone just outside their walls.
A Gemstone Cave is filled with concentrated gem deposits of one or more varieties and features a unique background (a gemstone wall) that is speckled with gems of the same color found in the Gemstone Cave. Unfortunately, the gemstone wall cannot be harvested and is instead destroyed by the hammer. Gemstone caves are found in the cavern and underworld levels, and unlike other treasure rooms are natural rather than artificial structures.
Sky Cabins are the main feature of a floating island. In 1.2 they were redesigned, changing from former brick shrines to colorful sky cabins with new blocks, new walls and unique furniture. The skyware chest inside contains treasure only found on floating islands.
The pyramid is a rare spawn in the desert. It is made of sandstone brick and contains narrow passages delving deep into the earth. The treasure room is filled with coins, vases and a gold chest that can have unique loot.