Deceit

Description
Deceit is a dungeon located on the small Janus Island, near Dagger Isle and north of Verity Isle. Dungeon Deceit is a horrible location. Not only is it home to many nasty monsters, like harpies and dragons who dislike intruders into their domain, but also a maze full of deadly traps and false leads. Many haven't returned from Deceit; their remains cluttering the corridors of the underground complex as a warning of the dangers that await in its depths. However, as horrible as Deceit is, it is also a good place to find good treasure.

Only experienced adventurers should dare to enter, or they will fare the same fate as all the others who had entered and never returned from its depths in their thirst for treasure.

Ultima IV
The Anti-Honesty dungeon of Deceit was first entered in Ultima IV. In it was found the Blue Stone, and a magic orb which gave one experience boost. It also connected to one of the Altar Rooms. It is unknown, why and for what purpose the dungeon was originally built. After the end of the Quest of the Avatar, the Great Council sealed the dungeon, to lock in the horrors within.

For a detailed solution, see: Solution for Deceit in Ultima IV

Ultima V
New monsters settled in the dungeon in Ultima V, when Deceit again was visited. The Avatar yelled the Word of Power "FALLAX", learned from Malifora, to open the entrance. The bottom level of Deceit connected to the Underworld, where the the Shard of Hatred was found.

For a detailed solution, see: Solution for Deceit in Ultima V

Ultima VI
In Ultima VI, there was nothing special about the dungeon,apart from loot.

For a detailed solution, see: Solution for Deceit in Ultima VI

Ultima VII
The Avatar entered Deceit in Ultima VII, because the Tetrahedron Generator of the Guardian, which was the the reason for the disrupted Ether, was housed there. Also, the Avatar met the cyclops Iskander and his pursuers Amanda(U7) and Eiko in Deceit.

For a detailed solution, see: Solution for Deceit in Ultima VII

Ultima IX
The Exit to Deceit was still on Janus Island in Ascension, however it is used as Blackthorn's prison. The caves you travel through are all filled with lava. The only way out is by teleporting, so its location is indiscernible.

For a detailed solution, see: Solution for Deceit in Ultima IX

Trivia

 * In Ultima V, the room that connects to the Underworld is split in two by a three tile thick wall. Inside this wall are five 1x1 rooms.  The center room has a Troll, the next two out Ettins, and the last two Dragons. The Ettins and Troll can be reached via Morning Star but the Dragons cannot; however, they can be charmed with the sixth circle spell.  Pushing the walls behind the torches is the way to get through.
 * In Ultima VI, Deceit is strangely enough a cave, while in Ultima VII, it isn't on Janus Island.