The mountains biome is likely the third biome you'll encounter in Valheim. This snowy hilly region is so cold that it will actually do damage to you when not near a fire, unless you have a wolf pelt or lox pelt equipped. If you're wet, it will do damage even with the pelt on.
Mountains biomes contain the following:
- Dragon Eggs
- Stone Golems
- Fenrings during night hours
Mountains are fun and all, but are bad places to build bases. You can do it, but it's going to be rough to not freeze to death, although with the pelts you should be okay. No reason you can't be ice faring mountain people in this game.