From publisher blurb:
A Pathfinder Compatible Adventure for 6th level characters.
This adventure is designed to be placed and run in any fantasy setting.
An ominious door sealed by both magical means and complex locks holds within an unknown evil, however the evil is spilling out into the world. Dare you breach the door and face the horrors that lurk beyond?
This adventure can be used as a follow-on from "ZS ADV03 The Missing Surveyors". Let your players find the door when they are low level, and then return when they have gained experience in order to open it and deal with what lies beyond.
There is no need to have run the previous adventure, this module is also completely stand alone, but it does add extra atmosphere to allow the players to come back and find out what was behind that mysterious door they found so long ago.