Sometimes, the spirits roam the Shadowlands without resting. It can be because their resting place wasn't complete, because of a battle in their resting place or because of the corruption of their resting place. To bring eternal peace to the souls, it is needed to destroy the source of corruption or by making a ceremony with items such as [Tuskarr Ritual Object]. A spirit in the Shadowlands can, with enough power over other souls, tear a hole into the living world once they are strong enough. This is how Jin'do returned to Azeroth.
Ascend the Tower of the Damned: at the heart of the Maw lies Torghast, Tower of the Damned, a cursed otherworldly prison where the wickedest souls in the universe are locked away. Highly replayable and inspired by roguelike games, heroes are invited to explore its ever-changing halls and chambers and do battle with the minions of the Jailer, Torghast's vile ruler. Those who brave its trials can claim legendary treasures and help free the heroic spirits wrongfully trapped within.
In classic World of Warcraft expansion "Wrath of the Lich King," Alliance soldier Bolvar Fordragon replaced Arthas Menethil as the avatar of the Lich King, ruler of the undead Scourge on Azeroth. Pledging to keep the ravenous dead at bay, Bolvar was sealed into the Frozen Throne, entombed in the haunted armor of the Lich King. It looks as though Bolvar is set to play a central role in the next WoW expansion, tentatively dubbed "Shadowlands."
The Shadowlands can be seen as a shadowy version of the physical world, and can be routinely visited as a spirit when player characters die. Governed by the Covenants, the four ruling realms of the Shadowlands are Bastion, Ardenweald, Revendreth and Maldraxxus (although countless others exist), which serve as the main setting of World of Warcraft's eighth expansion.