From the introduction: Castle of the Storm Gods is intended for four characters with an average party level (APL) of 16. Characters who complete this adventure should earn enough experience to reach halfway to 17th-level. A terrible storm has befallen the kingdom of Cressia, and at the center of it is a large floating castle. This campaign takes place in Arden, although it can be set in your own world. Any party composition should be able to finish the adventure with intelligent play.