This wiki has been moved to https://github.com/SuperTux/wiki into the mediawiki branch.
A possibility for another world is Water World or something like that.
Tux boards a ship, sails to a level in the middle of the ocean, and starts it by opening a bonus box and get a pirate hat and a pistol. The badguys are fish, seagulls, and pirate seals. Once Tux conquers the ship (in one level or a load of them) he can fight other ships, or stuff like that. It would be a great way to go between islands. Finally, after beating all the islands, he sails to wherever Nolok is.
The idea needs some more work, but feel free to build upon it. (And if the idea is used, I get to make at least one level in it, please?)