Krittannia, one of the first private sims to come online after Linden Lab began selling them, is the playground of Kris Ritter, and is predominantly themed Heaven & Hell. Hell resides inside the crater of a giant volcano that is the main feature of the island. Heaven floats on multiple cloud layers above the volcano. The sim is open to public use and Kris welcomes anyone to come hang out there :)
Some of the most respected builders in Second Life have provided content for Krittannia; much of Heaven was built by the mermaid Myradyl Muse. Gabriel, the single largest sculpture in SL, was created by Siggy Romulus. The event arena island in the south west corner of the sim, which is available for people to use upon request, was created by Eddie Escher and Fallingwater Cellardoor. Other contributors include SuluMor Romulus, Alpha Zaius, Lance LeFey, CrystalShard Foo and Tracy Murray. A credit board at the telehub area lists the full team and their achievements.
Heaven and Hell were deleted a few months after conception, being replaced by a "waterworld" type build. The sim was filled of water and structures built floating on top of it, similar in style to the movie Waterworld.
Later the sim was sold to Rickard Roentgen, who had plans to turn it into a nice residential sim with prebuilt homes. Mid-way through the project however Rickard decided to sell the sim which was bought by another resident, renamed, and now in use.
You can read more about Krittannia in New World Notes, NWN Link: Krittannia Coverage