Isle of Fire

Description
The Isle of Fire is a desolate land mass, famous for housing the diabolical daemon-machine Exodus. A rocky and inhospitable place, the isle has risen from the Great Sea twice in Britannian history: the first when Exodus first began his campaign of vengeance against ancient Sosaria, and the second when the mage Erethian lifted it from the sea in the course of studying the hellspawn's Dark Core. Although this place has been long stained with the infamy of evil, Lord British nevertheless attempted to bring something of the Virtues to this lonely place, establishing three great Shrines to the Principles upon it.

The island, itself, is dominated by the Castle of Fire, at times known as "Castle Death." This dark fortress once served as Exodus' stronghold, with daemons and other servitors of darkness patrolling its hallways. It is here that the daemon-machine was confronted by the Stranger and met its end.

Age of Darkness
The Isle of Fire first arose some twenty years after the death of Minax, coming into existence once Exodus was ready to invade Sosaria. From its fortress, Castle Death, the daemon-construct rallied armies of monsters to plague the realm of Sosaria, and a pirate armada to terrorize the seas. Its power waxed so great that it was able to wrest the Great Earth Serpent from the Void itself and install it as the island's guardian. Desperate to understand the evil that was festering in the Great Sea, Lord British sent Shamino to investigate the Isle of Fire and its keep, only to have his friend return to him overwhelmed with madness, his mind having been broken by what he'd seen.

Eventually, the Stranger's party was able to battle its way to the isle, passing the Great Earth Serpent and entering the castle. There, the Exotic Armour kept them safe from the fires brought to bear against them, and they tricked the machine into its own destruction using the Four Cards.

Age of Enlightenment
In the years that followed, Lord British endeavored to cast aside the barbarity that had marked the Age of Darkness and usher in a new era of enlightened learning and virtuous piety. Eager to establish some seed of righteousness in this place of abomination, Lord British ordered the construction of great shrines to the Principles of Truth, Love, and Courage on the Isle of Fire, hoping that someday a champion of the Virtues might find it a testing ground for their mettle. Before such quests could be embarked upon, however, the isle sank into the sea.

Age of Armageddon
The island and its castle remained under the sea for hundreds of years, yet during this time it was not closed to all who would explore it. Mages of great power, such as Erethian, Castambre, and Astelleron made their way to its shores, with the latter establishing a great air bubble around the isle, that mortals may survive there. Eventually, it was Erethian who uncovered the means to force the island to rise once again to the surface, having gleaned such knowledge from the Dark Core of Exodus, which still remained there.

The Avatar, now able to seek out the shrines, journeyed to the island on British's behalf. Solving the tests that still lay active on the islands shores, the hero eventually managed to banish the Dark Core into the Void that Exodus's resurrection might be averted—a move that drove the enraged Erethian to provoke his own death. While the isle still stood for some time after this final victory over the evil machine, it was not present during the Avatar's last journeys in the realm following the Great Cataclysm.

Ultima III

 * Exodus
 * The Great Earth Serpent

Ultima VII

 * Adjhar
 * Arcadion
 * Bollux
 * Dracothraxus
 * Erethian
 * Exodus's Dark Core

Trivia

 * Dr. Cat (David Shapiro) reports that he was given a copy of Ultima III a week before its release date in which a bug had set the maximum number of monsters appearing in each battle in Castle Death to one, making the endgame remarkably easy to complete.
 * In the Nintendo port of Ultima III, the Isle of Fire begins to sink immediately after the death of Exodus, and the final moments of game play involve controlling the party as they flee the crumbling castle.
 * In Seiji Tanaka's manga,  Ultima: The Terror of Exodus, Exodus' stronghold has a twisted Lovecraftian appearance, which showcases the machine-like qualities of both the daemon and its stronghold.
 * In the NES port of Ultima IV: Quest of the Avatar, the Silver Horn can be found here instead of on an island near Spiritwood.