The Bastion of the Triune, or simply the Triune, is an uberlevel accessible through the red portal that appears at the death of Lord Primus. On Hell difficulty, it is notably the only source of cycles in the game.
The White Temple of the Cult of the Triune. The symbol of the trinity is pervasive throughout their rank and architecture. Uldyssian broke the Templars' armies on the battlefield in his campaign to obliterate the Triune and the Cathedral of Light. Lilith, the Mother of Sanctuary, finally corrupted Uldyssian, and thereafter the Dark Edyrem sealed themselves away. Destroy Lucion to stop his plans to corrupt humanity.
Points of interest
The Triune is home to three bosses: Lucion, Malic and Durram. Lucion is the main boss, and can only be killed by Malic. In order to make them fight, players will need to acquire the Tome of Possession from Durram, which unlocks the Demonic Charm skill, and use it to charm Lucion.