Ice Machine

Two routes, arriving at very different points in a run. Frozen chests in the ice caves can hold one, which is the early option and pure luck, or the Steampunker will sell you one once she has moved in, provided you talk to her while she is standing inside a snow biome. The shop is reliable but late, so it is worth opening every frozen chest you walk past on the way down.

Building, and nothing else. It opens the frozen furniture line and the snow furniture line, both made from blocks you can dig up by the thousand in the same biome, so an ice themed house is one station away from being fully furnished. If you are not building one, it is a decoration that happens to glow in the dark.