Ultima Underworld 2: Labyrinth of Worlds

To commemorate the defeat of the Guardian's forces one year ago, you (the Avatar) and the leaders of Britannia are invited to Lord British's castle for an evening of celebration. Suddenly, the Guardian strikes again, encasing the building in a gigantic blackrock gem. He offers the imprisoned heroes a simple choice: proclaim him ruler of all Britannia, or starve while his minions conquer the land.