Infernus

The Infernal Dimensions are a number of worlds parallel to the world of Gielinor. The Infernal Dimensions are said to be the original home of the demon race, which first arrived in Gielinor during the Second Age to serve the god Zaros.

During The Golem, players travel to a small pocket of space where the Elder-Demon Thammaron once resided, and where he eventually launched a final assault on the city of Uzer in the Kharidian Desert. This may be part of an abandoned fortress in one of the Infernal Dimensions, although it is impossible to travel any further.