The "lost" Ultima game which Richard Garriott had no involvement in creating. Mt. Drash was long rumored to have been released by Sierra On-Line without his knowledge or consent, but this has been proven to be false; it was actually programmed by a friend of his, Keith Zabalaoui, and Garriott had allowed the name to be used as part of a deal with Sierra to get the game published.
Still, Sierra On-Line was doubtful about its chances of being a commercial success, having only one advertisement for the game run in magazines and giving it an extremely limited printing run. As a result, Mt. Drash sold very poorly and is now among the rarest video games ever created, with copies seen selling online for hundreds or even thousands of dollars.
In an effort to prevent counterfeit copies from surfacing on auction sites, a full image of the original tape has never been made available. The game has been made available through emulation as well as a fan port to the PC platform, however, so let's take a quick look.
(I did not create this video, but props to Georgc3 for enduring the music long enough to complete the game!)
As a couple extra bits of trivia, Mt. Drash is the name of one of the caverns in Ultima 1. The name of the game's villains, "Garrintrots", are most likely a corruption of Richard Garriott's last name.
Keith Zabalaoui also contributed to Ultima 2 and went on to become the president of Atomic Games, best known for creating the Close Combat series.
An article on the game from Hardcore Gaming 101
Another article on the game and the legend surrounding it