The World Tree YGGDRASIL had countless leaves, but then a gigantic monster appeared which devoured these leaves, causing them to fall one after the other, until only nine were left. These nine leaves were the previous incarnations of the Nine Worlds, particularly Niðavellir. However, the leaf-eating monster continued its advance to the point where it seeks to devour the leaf representing Niðavellir. This was the backstory upon which the players adventured into the world of Niðavellir in order to protect it.
Niðavellir was one of the realms where many players of the humanoid and demi-human races mainly resided in. By entering Niðavellir, players of the heteromorphic races are known to have disadvantages placed on them when faced by non-heteromorphic players.
The world was described to be ridiculously huge, and there were many places within it which were difficult to explore. For instance, there were many areas which required the use of special equipment along with a proper strategy and the determination in order to delve into its hard-to-find dungeons that drop valuable Data Crystals.
Within Niðavellir, things became more dangerous the further one went from the center of its world. In addition to the wandering monsters, the very terrain itself became a hazard for players to explore.
A developer-sanctioned tournament was held in this world where one could become a World Champion and acquired a special powerful equipment awarded as the winner's price for exclusive use with that class. Only one player with the World Champion job class was allow to exist in Niðavellir. There is also just one guild base in this world that contains 3000 levels of NPC Data Storage which is highest amount by far available.
- This world has its own particular traits, but they often shared one similarity which is the fact that it is two to three times the size of Tokyo.
- Some guild members of Ainz Ooal Gown had once thought of trying to conquer one of the worlds in YGGDRASIL.