Ring World is a four-piece puzzle. It is a two-piece sphere contained in a two-piece ring. The purpose is to take it apart. The puzzle can be split in half when when the ring and the sphere are properly aligned. This is a metal version. You can find a plastic version
here.
Watch the
YouTube video.
Read at the
Shapeways Forum.
Read more at the
Non-Twisty Puzzles Forum.
contact Oskar directly if you have any further questions.