In the Norse cosmology there are nine different worlds, connected to each other, worlds with their own fauna, natural landscapes and beings. Some see these worlds as separate planets, but in truth, the world is the same, but each continent is so vast, that it seems that each ream is a different world, with landscapes differing from each other.
We know of these places as the world of the gods, spirits and the dead, in other words, the afterlife. Through ages before history was recorded, certain humans had the ability to travel into these places, spiritual leaders of each tribe, shamans, who could travel in trance to these places, even today these kind of people exist and they can do the same work others did, so we might have a vast lore about the landscapes, the creatures and other beings that inhabit each realm. The Norse/Germanic people called the other world as the Nine worlds, and each world has its name and also lands within, but in truth it's just one huge world, the first to travel there by trance had the perception that it each landscape were different worlds because they didn't had the chance to stay there too long in order to travel from one continent to another, from land to land, and each time they visited, they were in just one, also in ancient times it was thought that the earth was flat and it would eventually end in a endless waterfall into the black abys of the surrounding universe, so this was also thought to happen in the other world, because traveling in certain continents eventually one would end up near the ocean, and this was why people thought that one world ended there and beyond started another one. Fortunately our knowledge of things grew, and as some of us can still travel to the other world by trance, we have a better perception of the landscapes, and we know that these worlds are all connected in one, oceans might divide one continent from another, but we know that rivers, forests and mountains also do, and by crossing those, we can reach the other realms.
As i have been talking here in my blog about all the other realms, i left Helheim as the last one on purpose, because it lies in the far south of the other world, but also because Helheim isn't what most people think it is, as you know, it is from Helheim or the goddess ruler of this realm, Hela/Hel, that the Christian Hell comes from, the scary, horrific place to scare people, but in truth, Helheim from the Norse mythology ins't such a place and i am about to describe it for you.