Isle of the Unknown is designed for use in any fantasy campaign.
The Island is nearly 35,000 square miles in area, making it larger than Scotland or Ireland. It features more than 300 hexes each of which contains a unique point of interest and none of the monsters, spells, magic items, etc. has appeared in any publication before this. The size of each hex (86 square miles) means that there's a good chance the a party of adventurers can pass through a hex without having anything other than mundane encounters.
Even though it has been written with a setting based on 13th century Auvergne in mind, this does not really come into play and can easily be adapted for any fantasy setting that the referee desires.
Written by Geoffrey McKinney, the author of Carcosa, this hardback book is lavishly illustrated in full colour throughout, with more than 120 illustrations depicting every monster that appears and many of the special spellcasters that are featured in the book.
You can read more about Geoffrey McKinney's thoughts on Isle of the Unknown here.