It was built on a newly emerged volcanic island—later to be known as Terfin—after Blackthorn was manipulated by the Shadowlords. The castle's position, centered between the isle's three volcanoes, corresponded with the location where the Avatar retrieved the Skull of Mondain from the seabed in Ultima IV.
The hero infiltrated the Palace of Blackthorn in Ultima V to retrieve the Crown of Lord British. After the end of Blackthorn's rule, its halls were left abandoned, but not for long; the mage Sutek assumed occupation in an effort to conduct his experiments undisturbed. The Avatar encountered the deranged wizard in Ultima VI while passing through the castle, hoping to find the balloonist with his plans.
In the midst of the volcanic fires, west of the hallowed Isle of the Avatar, a vast darkstone palace testifies to the awesome wealth and power that is now Lord Blackthorn's. In the few years since Blackthorn seized Britannia's throne and declared martial law, ostensibly to keep the peace in the land, his personal stronghold has grown to rival Castle Britannia in size and luxury. But there the semblence ends, for those who have had occasion to visit the Palace return - sometimes - with tales of great towers with seemingly bottomless pits, labyrinthine dungeons, nightmarish torture chambers, and daemonic guardians in the royal throne room. Half-human watchers patrol the endless halls, casting all who do not wear the Badge and speak the Password into the dungeon's torture chamber where lethal fates invariably await.