Vortex

Description
On the map of Elona:

The swirling Vortex, unleashed by the death of Varesh Ossa, leads to the Realm of Torment

On the map in the Realm of Torment:

The Vortex leads back to the mortal realm.

Basically, the vortex just lets players travel between the Mortal Realm and the Realm of Torment much like the boat icon that allows you to travel between continents.