Helheim (realm of Hel) or simply Hel, which means "hidden."
This is the land of the dead presided over by the goddess Hel. Some say a dog guards the entrance. Some say it is underground or in the cold and dark North.
Unlike the Christian Hell, the Norse Hel isn't for those who are being punished or those of morally outrageous conduct. The Norse Hel is a place where the dead live on, pretty much doing what they were doing in their alive states.