Gnolls of the Bleached Skull

From publisher blurb:

The depraved gnoll shaman Grirr Duskclaw lurks in the lightless dungeon below the Hill of the Sunken Skull. There in the endless dark, he toils over the blasphemous, blood-soaked creation of a legion of bloodspawn treants he plans to unleash on the nearby human settlements. A chance discovery leads to the characters learning of the Hill of the Sunken Skull, but not the horrors lurking beneath, and sets them on the path to bloody confrontation and death.

Designed for The Lonely Coast but easily adapted for virtually any other setting.

This System Neutral Monstrous Delve presents the atavistic gnolls of the Bleached Skull tribe, along with a detailed overview of the dungeon below the Hill of the Sunken Skull.