Demon Realm

The demon dimension is an alternate plane, much like the Spectral Realm in that it was coterminous with the material realm. We only get a brief glimpse of the place when the Heart of Darkness is torn out of Kain's chest, yet he awakes in the demon dimension for some reason as he is shown pushed into a portal inexplicably.

The natives of the Demon Dimension are, unsurprisingly, the various species of demons. The hylden are also residents of the demon dimension since they were banished there by the ancients and kept there because of the pillars of Nosgoth.

The Demon Realm is kept seperate from Nosgoth's Material Realm by The Pillars after the Hylden's creation The Device defys many Natural Laws and unbalances the Dimension's and the barriers that spereate them.

In Nosgoth's future distant Future Demon's were shown as fairly common and Human's had adapted to combat them.