Skullcrusher

Description
On the Serpent Isle, north of the Northern Forest, deep inside the mountains lies the ancient Ophidian city of Skullcrusher, the city dedicated to Chaos.

In the time of Ultima I, the dungeon was known as Skull Smasher, and not remarkable. However, after the three serpents appeared, the city of Chaos was built within the dungeon, housing at its lowest point the Shrine of Chaos. The city stood as the opposite to Spinebreaker, the city of Order. When the War of Imbalance went into its final phase, the forces of Order stormed the city, killing everyone and destroyed a good part of it. Afterwards, the city became forgotten.

Much later the the vampire Vasculio took up residence in the city, using it as his base. After he was killed by the Avatar in Ultima VII Part Two, the Avatar opened the gate to the shrine, to re-create the Chaos Serpent. Leaving, the Avatar let the ruins of the city finally rest.

Things to see

 * Shrine of Chaos

Trivia

 * There are big locked doors to the east. There's no key that can open them, but you can get through with HackMover or Exult's teleport cheat. There is not much to see here, though - a few mostly empty rooms and a set of stairs that lead to the middle of what appears to be ocean. It's possible developers intended to add something to this area, but it was left unfinished due to the rushed schedule.
 * There really isn't much left of the city, since the forces of Order did a good job at destroying it.