The Chaos Temple (AKA Zamorak Temple) in the Wilderness is a Temple of Zamorak located around level 14 Wilderness, north of Varrock. The temple is accessible only from the north, as the entire building is near-completely surrounded by molten lava.
There is a trapdoor behind the altar that is part of the Defender of Varrock quest.
The Chaos Temple contains an altar which members may use to offer bones for Prayer experience. Using bones or ashes on the altar gives 350% of the Prayer experience that would be gained by burying or scattering them, equivalent to the Prayer experience bonus given by a gilded altar with both incense burners lit.
Players can use Simon who is just on the other side of the temple walls to bank and restock on bones. Roughly 1,400 bones can be offered an hour without the need of a BoB using this method, this makes it about equal to using a pack yak in POH.
Players who have completed the hard Wilderness Tasks will be able to un-note bones from their inventory with Harrison who is located within steps of the Chaos Altar. Doing so will reduce time per run and increase the bones per hour to roughly 2000.
The area contains many spawns of bones. Free players may use these bone spawn points at a lower prayer level to raise Prayer, especially if the player has low combat and cannot efficiently raise prayer from killing monsters which drop big bones such as hill giants.
The pattern on the floor hints that the temple may once have been dedicated to Zaros, which is plausible given that many of his fortresses and outposts in the second age were in what is now the Wilderness, and were destroyed and/or aligned to different Gods during and after the God wars.
During the Third Age, was a Zarosian temple as shown in the "Saradomin Strikes" campaign. Several gods, such as the Menaphite Pantheon, Saradomin, Bandos, Zamorak and Zaros fought for a powerful artefacts kept inside the temple. After a long battle Saradomin eventually came out as the victor and claimed the artefact. It is possible that this artefact is in fact the Relic.