Ultima VIII: The Lost Vale

 The Lost Vale is a vaporware product. It was planned as an add-on for Ultima VIII: Pagan. The big doors on the Plateau most likely were planned to be the entrance. Electronic Arts, disappointed with the poor sales of Ultima VIII, pulled the plug on the project, despite it being practically finished. Only some screenshots and the box design (which was later confirmed as the real deal) survived.

As far as it can be reconstructed, the Titans had sealed their enemies, possibly the 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 on his quest to leave Pagan. No more is known about the story. But from the screenshots, some material can be interpreted:
 * 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' legions of undead appear also.
 * According to the box, a "bag of reagents" was supposed to appear, ending the need for finding reagents (like the Ring of Reagents did).

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

Story
Around 2007, more details of the story came to the light:

''The story of Lost Vale was that a group of people had been shut off from the main population of Pagan when the Ancient Gods disappeared. They were isolated for a very long time. However, during this isolation a terrible tragedy involving the deaths of two young boys had befallen them. This tragedy caused a schism in the population with each side blaming the other for the deaths. Neither side had spoken to the other for a decade. It was up to the player to “awaken” the Ancient Gods and heal the schism between the people. To do this, the player had to ascend to the very cloud city where the Ancient Gods were believed to live. There, a terrible surprise was uncovered. The Ancient Gods were not asleep, but actually had been imprisoned. The player had to figure out how to release them. The cloud city appeared abandoned, but was full of traps and tricks and was very dangerous.''

''As a side note, it was for this add-on disk that the “tiny-tar” spell was developed. This was a spell the player would be able to cast upon him/herself and make themselves shrink. I believe this was developed by John Watson. We got such a kick out of a teeny tiny avatar running around the world that we worked it into the plot line. At one point, to get into the ruined temple, the player had to cast the tiny-tar spell and creep in through a crack in the wall. Great fun!''