Instructions
Defeat the Marquis Montalban several times in one-on-one duels. Governors and rumormongers may be able to tell you where Montalban is hiding out if you do enough favors for them.
Collect map pieces from Montalban after every defeat. The map pieces will combine to show you the way to his hidden fortress.
Sail to the location on the map and disembark to walk the lands on foot.
Follow the map markers -- geysers, totem poles and Indian ruins -- until they lead you right to the fortress.