Underused Biomes for RPGs

Biomes - environments that fall into a certain category - are a great way to set the atmosphere for a specific adventure. We all know of deserts, forests, swamps, mountains, and so forth, and each of these biomes have their own iconic adventures and adventure sites.

But the real world is full of obscure, unique environments that aren't known to many people - let alone #ttrpg players, which makes them a great option to bring variety to a game - and fantasy and science fiction has come up with all sorts of further biomes that aren't known on Earth. So what are your favorite obscure biomes?

Personally, I am fascinated by so-called "Cloud Forests" ever since I heard of the concept. They are usual tropical or subtropical forests which, due to their geographic locations, are shrouded in fogs for much of the year. In RPG settings, forests often hide many dangers due to their low visibility - and so does fog. It's two great tastes that go well together!