I came across these interesting, old cameras and was about to throw them out. Then I tried opening one and realized they could be repurposed as geocaches.
It's up to you to figure out how to open them and record your signature on the "film" inside. Close and replace as you found it. I do not have more of these so once they're gone or muggled, that's it.
Gur ynetr ebggra gerr yrnaf ntnvafg 2 fznyyre gerrf, purpx gurer.