I started geocaching a month or so back, and have been putting out a few caches myself as well. I’ve been looking through forum threads with cache ideas, and one that really stuck was the idea of a cryptex.

A cryptex is basically a container with a code lock. You have two inner tubes- in my case from a vacuum cleaner- where one goes inside the other. The inner tube has knobs on it that slide into a cut out track in the outer tube. You then slide discs (made of wood in my case) onto the outer tube, which each have one small groove that lets the knob from the inner tube slide through. The inner tube will then only be able to slide all the way out when all the grooves in the discs line up perfectly. Add some symbols to the discs and you can make a specific code that also lines up the grooves.