Ultima VIII: The Lost Vale

A vapor-ware product. It was planned that there would be a add-in disk for Ultima VIII, "The Lost Vale". The big doors on the Plateau most likely were planned to be the entrance. Sadly, Electronic Arts, disappointed with the poor sales of Ultima VIII, pulled the plug on the project. Only some screenshots and the box design survived.

As far as it can be reconstructed, the Titans had sealed their enemies, most likely Zealans, in the Lost Vale, together with three of the Gods of Emotion: Felicitar, Doloras and Timyra. The Avatar would have the duty to release these three Gods, so that they help him/her on the quest to leave Pagan. Much more, sadly, isn't know about the story. But from the screenshots, some facts can be recovered:
 * The three Gods, who are mentioned in a book at the entrance to the Shrine, are trapped in force fields, and have to be released.
 * Part of the action is high in the mountains, with clouds around.
 * Hydros' legion of own undead appears also.
 * Accoding to the box, a "Bag of Reagent" was supposed to appear, ending the need for finding reagents (like the Ring of Reagents).

Possible entry point
Most fans speculate that the entry point to this quest are the double doors in Plateau. In ordinary game, these doors cannot be opened; it's possible that something was planned for these doors. The doors also have a lot of human remains; it is possible this was some kind of a site of a great battle.