This is my take on the classic Oliver String Puzzle. The one shown was built from scrap wood, a ring from a previous project, purchased wood beads and rope.
Build Instructions: https://www.instructables.com/id/Oliver-String-Puzzle/
I've included STL files for those that would like to print it.
If neither of those work for you, you can buy a similar version from Amazon: http://amzn.to/2B1Rkni
The goal is to remove the ring from the puzzle. My kids and wife found it quite challenging. I would rate the skill level at 3 out 5. If you can't figure it out from the pictures, refer to the video.