The room where the orb that contained The Power was located.
The altar room is a large room with many hieroglyphs describing the curse of the castle. Romanov was seen observing these, and they appear to contain a warning, since he wanted to leave immediately after reading them.
At the top of the altar a power struggle between Etrius and the General occurred, when the power entered Etrius' mind and started talking for him. The General shot him to obtain the orb, while Evils started flooding the room. The doors were sealed, and the elite team sprang into action. Beecher went to check on Etrius, while the General ran down the altar and was confronted by Lloyd, before being interrupted by the enemies.
In the ensuing chaos of the attack, and the chasm spreading across the ground, Lloyd was trapped in the altar room with the enemies, along with Etrius' unconscious body. It is currently unknown what happened to them, though Lloyd appeared several times, possibly as a mirage, to haunt the soldiers trapped in the Castle. A demonic voice also calls out "Llllooooooooyyyyyddddd" several times from the altar room. At the end of Repercussions, Etrius' body is shown to be missing from the altar, suggesting he is still alive.