This realm is where all who die from disease, old age or other causes without having accomplished something worthy of honor go to in the afterlife.
Helheim is located mostly underground, and the long road from Svartalfheim to Hel's domains is called Hellway, where only darkness rules. The only light here can be found at the end, where the glittering, golden Gallarbridge crosses the river Gall (the thundering waters). The bridge is guarded by the surprisingly good hearted Modgunn, who asks everyone crossing the bridge why they would wish to enter Hel's domain.
Hellgate is the name of the final gate blocking the way into Hel's great halls of death, and it is guarded by the great hound Garm. Only when the Hellgate is opened can the tormented souls and undead escape to pester and haunt the living. At the end times (Ragnarok), this gate will be blown wide open, and release the undead armies within.
In Hel's domain one is always cold and hungry, even in the food courts known as Eljudne (the damp halls). Only terror and torment is to be expected in this terrible realm.