The Ancient altar is built in the Achievement Gallery of a player-owned house as a place where players can switch their spellbook to Ancient Magicks. Other players can use the altar, provided they have completed Desert Treasure.
Unlike the altar found in the Jaldraocht Pyramid, switching spellbooks at this altar will not drain the player’s prayer points.
The lowest level at which the altar can be built is 75 Construction, using the +5 boost from a spicy stew. The crystal saw cannot be used to lower this requirement, as the Achievement Gallery room requires 80 Construction and is unaffected by the saw.