From Introduction:
The Pit of Loch-Durnan is an adventure compatible with the d20 system for 3 to 6 characters ranging from 2nd to 4th level. This adventure takes place in the small hamlet of Loch-Durnan, a town where two sons of the former mayor have fallen on dark ways, and have come to serve an imprisoned evil beast who seeks his release. The pair has sworn to assist the devil in his escape from the powerful crystal he is trapped in under a small mine called the Pit of Loch-Durnan. They can only do this by expanding the influence of the devil’s power.
This is a multi-part site-based adventure that should take the party up a level or two. It is designed with five 2nd-level characters in mind, but you can adjust it to accommodate three or four 3rd- or 4th-level characters, etc.