From publisher blurb:
The Hidden City is a d20 adventure, taking place two years after the events of the The Witchfire Trilogy. It has been designed for four to five characters of levels 8-9.
Following trains of human slaves Harven soon tracks down the Skorne to the Rotterhorn Mountain where he finds a large citadel. It seems the Skorne have been here for some time.
This scenario is available as a free download. Each chapter is downloadable as a separate file.