Sphere Generator

The Sphere Generator is one of the three colossal blackrock structures utilized by the Guardian to prepare Britannia for his coming in Ultima VII.

Description
Appearing sometime after the founding of the Fellowship approximately twenty years prior to the Astronomical Alignment, the Sphere Generator created a space-time trap, such that the Time Lord, who was eager to obstruct the Guardian's plans, would remain imprisoned within the Shrine of Spirituality. In addition to this function, the construct also disrupted the workings of the realm's moongates, causing the portals to grow unstable and dangerous.

Located deep within Dungeon Despise, this generator was protected by a red moongate, which transported anyone who attempted to approach the construct several yards away from their intended destination. In order to breach this defense and access the interior of the black sphere, the Avatar would have to possess a specially Enchanted Hourglass which had been prepared by the mage Nicodemus. Armed with this artifact, the hero would be able to enter the blackrock construct, where they would find a surreal maze of interconnected moongates and flames. Once they navigated to the center of this labyrinth, however, they would be able to retrieve the miniature sphere-shaped prism from within the generator, thereby precipitating its destruction.

While its destruction freed the Time Lord, the Guardian had built-in a safeguard to spite whoever would destroy the generator. This safeguard permanently shut down all moongates, effectively stranding the Avatar on Britannia.

Trivia

 * According to the Time Lord, the three blackrock generators were sent to Britannia from the Guardian's home-world; indeed, while developing, Richard Garriott envisaged Britannia's would-be conqueror to have originated from a race of omniscient, godlike entities who might themselves eventually become antagonists in the series. This, however, would later be superseded by Ultima IX: Ascension, in which it is stated the Guardian coalesced out of darkness purged from the Avatar in the final moments of Ultima IV: Quest of the Avatar.
 * The shapes of the three generators (a cube, sphere, and tetrahedron) form the logo used by Electronic Arts from 1982 to 1999. Richard Garriott has since given conflicting statements, both denial and confirmation, as to whether this was conceived as intentional symbolism.
 * It actually is possible to carefully squeeze yourself past the moongate on the right side. Doing so short-circuits the plot.
 * In the SNES Port of Ultima VII, the Sphere Generator had no inner defenses, and will self destruct the moment the Avatar moves its corresponding prism from a nearby pedestal.