Wooden puzzle. Laser cut.

thingiverse

To crack this puzzle, you'll need to liberate the ring. Unfortunately, I didn't jot down the solution itself - it's a bit straightforward, but I'll have to ponder on it for a moment. Nonetheless, rest assured that the answer is 100% guaranteed. For starters, you'll require some plywood, preferably 4mm thick. Alternatively, you could opt for 3 or 5mm thickness - the design isn't particularly finicky about the material's thickness. You'll also need a small amount of glue to hold everything in place. A clothesline measuring approximately 40 cm will serve as the primary component. To prevent the rope from slipping into the holes, simply tie knots at each end. As for the ring itself, a 3cm diameter will suffice. If you can't find one, feel free to cut it out of plywood - it's not a complicated process.