Wizards of the Coast put out free monthly “Original Adventures”
to support D&D 3.5. This review covers the seventh of that
series, Eric Haddock's Lochfell's Secret, recommended for 15th-level
adventurers. Like the Original Adventures that I've reviewed so far,
this module only requires the core rules (PHB, DMG, and MM) and is
compatible with Pathfinder (using the Core Rules and Bestiary).
Lochfell's Secret also showcases some non-core WotC content,
providing the full mechanics but only short descriptions. The
missing details shouldn't substantially affect the enjoyment of the
adventure and it's actually a good opportunity for the DM to
improvise. The work is no longer available for free, but for $0.99 you can get a copy of Lochfell's Secret.