I sometimes wonder why there are so few actual gaols in D&D - most PCs I know belong behind bars! Try this one for size... It's the classic 'stuck on a remote island' variety of gaol, and of course you can tuck it in any suitably remote and inhospitable corner of your campaign world.
Publisher's blurb: "Far from land, where no man dares to tread, lies an island prison, where only the foulest reprobates belong. It is Hell's Reach. Surrounded by sharks, infested with dregs, and banished for all of time, those sent to Hell's Reach never return. A fully detailed city for any level of adventure."
Author: Mike Mearls
Publishers' Reference: AEG8338
Paperback, 16 pages
Date: December 2001