Ultima VI: The False Prophet/The Codex and the Vortex

The Shrine of the Codex
Back to the Temple of Singularity, say the mantra of Singularity. The shrine will then set you on the quest to the Codex.

Cross Dungeon Hythloth all the way back to Britannia. From the Shrine of Humility, go north across the lake on the Isle of the Avatar. The statues will let you pass now. Read the Codex of Ultimate wisdom. It says that you need not only the two lenses, but also the Vortex Cube and the eight Moonstones.

Stonegate
About the Cube, the Caretaker said: "To regret that that item is lost, stolen by human thieves years ago. To have heard the humans mention the name Stonegate as they fled. To have heard them say they would sail through Lost Hope Bay. To know nothing more about its whereabouts."

Lost Hope Bay is exactly south from Minoc, and Stonegate is at its southern end.

Talk to Myles, Papa and Mama. Papa will ask you to bring him a fish. If you need a fishing pole, you can get the one in the fortress. When you bring him a fish, he will give you the key "H" in return.

There is a small room at the center of the fortress: look for the secret passage. That is the entrance to Stonegate cellar. In the small secret room, operate the four levers. Get back upstairs, then down again from any of the four ladders. The levers removed eight portcullises, and you can now go downstairs. Take any of the ladders in the corners, except for the north-west one: it is a dead end. This floor is made of four identical quadrants. In each of them there is a ladder down (except for the north-west one). Similar to upstairs, there is a secret room at the center. Operate the switch in there and deactivate the electric fields. In the north-west room there is another secret door. There are poison fields beyond it, therefore cast "Dispel Magic" to pass. Use the key from the cyclops to open the door. One more "Dispel Field", and you can get the Vortex Cube.
 * Floor 1
 * Floor 2
 * Floor 3
 * Floor 4

The Vortex
Once you collected the two lenses, the eight Moonstones and the Vortex Cube, go back to the Shrine of the Codex and follow the instructions written on the book. Use then the Vortex Cube, and enjoy the ending of Ultima VI.