The Orb Chamber is the final room of Amnesia: The Dark Descent. The Chamber lies at the very heart of Brennenburg Castle and is also the deepest room into the ground. It is Alexander's most precious and hallowed of all chambers.
The Chamber is accessible from the Inner Sanctum (of which it is also a part of). It was seemingly built for the sole purpose of allowing Alexander to return to his own world and, as such, is very utilitarian in this regard. Both the Orb Chamber and the Inner Sanctum are all but impenetrable while the chamber is guested by an Orb. Only the power of another can overwhelm the barrier around it, allowing entry.
Alexander is trying to utilize the power of the Orb brought by Daniel, to open a portal. The Orb's energy is channeled through three pylons containing the vitae taken from countless people tortured to death. These structures surround a central altar upon which the portal forms. When the ritual commences, the Orb tears a rip in space and time, creathing thus an interdimensional portal that can allow one to pass from this world into another. It is here, at last, where Alexander is found: levitating nude in the air, while performing the portal-opening ritual. He is up on a raised platform surrounded by blue flames that prevent Daniel from getting close to him. Behind Alexander strange (possibly occult) writing can be found on a tall, slender stone as well on the frontal side of the platform he's standing on. Up near the ceiling, there are numerous rocks suspended in midair circling the portal device.
Before the events of the Dark Descent, Alexander was fearful of Wilhelm and his men, who might betray him to the Law, so he proceeded with the final ritual without proper foresight in using these relics. He accidentally cracked Agrippa's recovered Orb and it fell into six parts. Alexander tried everything, but was unable to mend it.
Later, at Alexander's response to his letter, Daniel fled London for Brennenburg hoping that the baron might be able to help him escape from the Shadow following him. Alexander convinced him that together they could banish this guardian forever in a ritual. This was a lie. The true purpose of the Inner Sanctum and Orb Chamber however had always been to tame the power of the Orbs, forcing them to yield. Daniel unaware of this, put all of his hope and faith in the Baron's abilities to liberate him from this ancient horror.
On the 8th of August 1839 Alexander took Daniel into the Orb Chamber and tampered with the relic. The invisible Shadow was angered and its fleshy residue materialized. Alexander covered the Orb to prevent it from consuming him. Alexander also told naive Daniel that the nightmarish force was closer than he thought. He used this excuse to get Daniel to cooperate with him in extracting and gathering vitae from the prisoners to complete his "ritual".
It is later revealed in a letter that Alexander knew, and even possibly regretted, the fact that he could not bring Daniel with him once the ritual was completed, even if they had acquired enough energy to allow two to enter. Alexander wrote that he found it ironic that he would have to do the same thing to Daniel, that Agrippa and Johann Weyer had done to him years before. Alexander believed Daniel has been "branded" by the Shadow from the beginning, and that the nightmare would follow Daniel wherever he could go. It is possible that Daniel had been marked for death because of the baron's meddling. When Alexander had the ignorant young man gather the last of the required amount of the vitae, he stole Daniel's Orb and abandoned him, leaving a furious and grief-stricken archeologist as an offering to the vengeful and bloodthirsty Guardian.
Eventually Daniel, who had already destroyed his memories with the amnesia mixture, arrives to confront the Baron. He finds and rebuilds Agrippa's Orb to remove the barriers to the chamber. Using his own blood he breaks the final seal placed on the doors.
Once inside, Daniel can opt to do several things that will result in three different endings. If he allows the ritual to take place, either by doing nothing and watching Alexander's escape or throwing Agrippa's head through the portal, the wrathful Shadow will consume him for abusing the artifact's power, though if he throws the Agrippa's head through the portal, the ending implies that Daniel is then rescued by Agrippa and Johann Weyer. Lastly, he can choose to avenge his former self and the deaths of all the killed innocents, by pushing over the three unstable pylons. This messes up the ritual. The satisfied Shadow almost immediately devoures Alexander as an atonement, but leaves Daniel alone and free to go with a guiltless conscience. The last scene in the game (after pushing the pylons down) shows as Daniel is walking out of the castle; hearing it crumble behind as he leaves unharmed.
- Alexander states that the purpose of his machine is to emulate a Traveller's Locket, which allow the owner to travel through different worlds.
- The interior and walls look much older than the rest of Castle Brennenburg. It is possible that this chamber is a genuine Mithraeum, a place of worship in Mithraism, and the same one where Agrippa found his first Orb.
Amnesia The Dark Descent: Brennenburg Castle - Rainy Hall - Old Archives - Entrance Hall - Archives - Wine Cellar - Laboratory - Refinery - Cellar Archives - Archive Tunnels - Back Hall - Study - Guest Room - Storage - Machine Room - Elevator - Prison: Southern Block - Prison: Northern Block - Cistern Entrance - Cistern - Morgue - Control Room - Sewer - Nave - Cells - Choir Entrance - Choir - Main Hall - Transept - Chancel - Inner Sanctum - Orb Chamber