Palace of Blackthorn

The Palace of Blackthorn was the stronghold of darkness from whence Lord Blackthorn ruled over Britannia in the absence of Lord British. The castle itself was intentionally built as a maze to confuse intruders and teemed with foul creatures, members of the Oppression, and traps.

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.

Refugees from their condemned homeland, the gargoyles later founded an entirely new city upon the site, after which all traces of the palace ruins had vanished by the time of Ultima VII.

Trivia

 * Entering the castle without the Black Badge in Ultima V was a really bad idea.
 * Batlin still describes the ruins in The Book of Fellowship, which was written some years prior to Ultima VII, giving a rough point in time for when the ruins vanished.