Niflheim

Niflheim ("house of mists") is the far northern region of icy fogs and mists, darkness and cold. It is situated on the lowest level of the universe.

The realm of death, Helheim is part of the vast, cold region. Niflheim lies underneath the third root of Yggdrasil, close to the spring Hvergelmir ("roaring cauldron").

Also situated on this level is Nastrond, the Shore of Corpses, where the serpent Nidhogg eats corpses and gnaws on the roots of Yggdrasil.

After Ragnarok, there will be a hall here for the punishment of murderers, oath breakers, and philanderers

Source: the Encyclopedia Mythica, please visit their site for much more