Realm of Hel.
Known to be the lowest and final of Nine Realms in Norse Mythology. The realm is known to be final destination and resting place of the dead. The realm is also known to be described as underworld as in details it was also known for the place for the dead who did not died in the battle.
In some poetic lines, Hel was believed to be below the roots of Yggdrasil (which presents roots in sketches) while also known to be dark cold place like the goddess(Hel) herself.