The Cauldron is one of the Fertile Lands in Prince of Persia and can be reached from King's Bounty. It is guarded by a Corrupted known as The Alchemist, a red insectoid creature with the power to control the ebb and flow of Corruption.
Before being cleansed, The Cauldron contains many pipes and lots of vines, along with a deep pool of Corruption at the bottom. When spoken to, Elika explains that when Ahriman took the city from the Ahura, a Corrupted called The Alchemist made his prisoners build the pipes in The Cauldron and performed experiments on them in the name of science.
The Cauldron is so named probably because of its shape which makes it appear as though you are inside a large pot - when it is corrupted, The Cauldron has a pool of Corruption at the bottom that rises up like it is boiling up out of a large Cauldron, and you must out run it as you make your way to the top where the Fertile Land, and The Alchemist, await.