The Matron's Den is a crypt-style area appearing during the Pandemonium Event. It can be unlocked by transmuting the tree three keys ([[Key of Hate]], [[Key of Destruction]] and [[Key of Terror]]) in the Horadric Cube while in Harrogath, making a red portal to appear. Its only purpose is to serve as home for Lilith, who must be killed to get [[Diablo's Horn]].