Borealis
Mysterious icy charges—Hailstones—have begun to fall from the sky in cold places. Leaping past the top of the world (with Jump Boost, a Wind Charge, or any other way you can think of) with a Hailstone's insulation protects you as you transition from the Overworld to an entirely new world in the freezing stratosphere.
Borealis is unique among dimensions in that it is uncharted: you will not find any manmade structures or ruins here, as mankind has never visited. Nevertheless, Borealis hosts a plethora of ancient animals, plants, and ecosystems, which have survived in subtly-sustained balance for millennia.
You must take care not to disrupt this balance, for it has never known human touch. Otherwise, you might find nature itself fighting back as its last effort before total collapse. However, Borealis does bear precious minerals and materials that you may want to bring home.
Hailstones are your ticket in and out of the dimension, protecting you from drastic temperature changes as you fall down into the void or rise up above build height. If you want to establish a more permanent Portal, fiber-optic Kyanite Cables, made from six Kyanite Crystals each, arranged like so can be lit in its center with a Hailstone, too. A lit portal's frame transforms into the otherwise unobtainable Kyanite Flagstone. Borealis Portals always link to the highest portal at the exact same coordinates in Borealis.
Biomes
Boreal Tundra
The Boreal Tundra is barren and fully exposed to the elements. Hardly anything survives here; it is what the forests become when disturbed to ecological collapse. Creatures here will leave you alone if you leave them alone; but they learn quickly.
Brumal Grove
The Brumal Grove is the home of prehistoric plants and animals, distantly related to those you might dig up in the Overworld. Its undergrowth ecosystem is vulnerable to light and rapidly dies out without the cover of trees.
The Frostfir
Three intelligent beasts vie for control of the dark forest of the Frostfir. By hunting or helping them, you can reap significant benefits at the cost of the balance of the forest.
Saccharine Hills
This biome is made to be eaten! Made entirely of sugary forms of useful materials, it's hard not to run through at breakneck speeds, mining everything you see.
Ravaged Glacier
Buried underneath the protective icy surface, creatures lurk and thrive in the dark. Deciding to unearth them could be dangerous—for both of you.
Hot Spring Islands
Endless fun is to be had in the Hot Spring Islands, bouncing high up with geysers and landing safely in floating pools or on steaming clouds. And don't worry if you miss: brittle pumice will break your fall, as will the soft mineral clays dissolved under the hot spring water.
⚠️ Borealis is a work-in-progress mod. It is currently playable but not in any complete form.