The Moon surface.
The Moon Biome is a very cold planet type made up of Moondust, Moon Rock, and Moonstone. This planet type is considered very dangerous because of its low temperatures at night and unbreathable atmosphere, but compensates for this with an exceptionally high output of resources.
Survival in the biome requires an equipped Survival System and either frequent use of Torches, Campfires and Old Radiators or extremely high-warmth gear, such as the Snow Infantry armor or Impervium-based armors. Once far enough underground, however, the temperature and atmosphere will return to normal. The reason for this is unknown.
Gallery
An Airship on the Moon!