The Dark Altar is a unique altar located in the Arceuus House, which allows dense essence blocks to become infested and turn into dark essence blocks, which requires 100% favour with the Arceuus House. These dark essence blocks can then be used with a chisel and crushed into dark essence fragments. Each dark essence block is equivalent to 4 pieces of essence.
The Dark Altar's origins and age are unknown, yet it has been studied by the inhabitants of the Arceuus House for as long as their documented history. The Dark Altar's power is near-limitless, and the full extent of its power remains largely unknown, even by those who have studied it extensively.
According to Amon Ducot, the author of the transvergence theory, it has the ability to bring life out of death when reanimating corpses, corrupt individuals and break minds. In addition, its power allows it to bridge the gap between life and death, sanity and insanity, as well as converging the dimensions needed to craft runes.
It is known that its power created the blood and soul altar located near it by drawing energy from the planes where the real altars are located. This power enables the souls of Great Kourend's dead to be transported to the River of Souls, where they are brought to the afterlife.
Although not visible in-game, it is known that texts of an ancient language are inscribed on the Dark Altar, which contains a recurring symbol that translates to sacrifice, although it may also be interpreted as death.
- Transportation incantations, Old School RuneScape. "Our blood and soul altars are focal points where the energy comes into this dimension from the true Blood and Soul Altars, wherever they may be."
- Soul journey, Old School RuneScape. "...the soul altar enables our city's departed souls to have the comforting certainty of the River; it is clearly a great blessing..."
- Ricktor's diary (7), Old School RuneScape. "One word keeps appearing in all of the text I read, sacrifice. I do not yet know under what terms the word should be used, I must study further to understand more."
- Ricktor's diary (7), Old School RuneScape. "His understanding of the language is beyond laughable and his translation of the symbol as 'death' rather than 'sacrifice', is simply absurd."