Planescape - Something Wild

From the web:

Something Wild is a PLANESCAPE adventure for four to six characters of 4th to 7th levels. When Sigil falls prey to disturbing nightmares and outbreaks of violent fury, the heroes must follow bloody trails to the treacherous peaks of Carceri and the savage jungles of the Beastlands. An ancient terror threatens the planes anew, and only the player characters can stop it from feasting on the flesh of the multiverse.