Oxedale Fort

From publisher blurb:

Hey, Traveler! This is the tenth installment of the brochure adventure series. Following the same train of thought of the one-page dungeons, these are system-neutral and easy to adapt to any system.

In this adventure, the characters visit a fortress on a mountain's skirts that has been taken by gnolls; most of the garrison perished during this attack. The characters are tasked with recovering the fort from the hyena-folk to recover some of the territory lost to the gnolls. In there, the characters soon realize that the gnolls are up to no good. The gnolls draw blood circles and chant as they celebrate a demon-summoning ritual. They must be stopped at once!