The ancient Prayer lamp is an additional reward from The Death of Chivalry, that requires 80 strength and 65 prayer to claim. It can be found by opening and searching one of the coffins in the room of the crypt where Dawn was fought. It grants 60,000 prayer experience upon use. If you die in the wilderness with this lamp in your inventory, it will respawn in the coffin where you found it after the quest.
The update history project is a work-in-progress – not all updates to this topic may be covered below. See here for how to help out!