So I attend this local annual event that has a time capsule. Each year, we bury one and dig up the one from 5 years ago. This has gone on for several decades, and people are always thinking of interesting things to put in there.

I made a little electronics project that is somewhere between "what happens inside a time capsule while it's buried?" and "what if you could wind a watch once and have it still be ticking in 5 years?"

I nearly forgot that I made a project page for it: https://hackaday.io/project/160740-low-power-environment-mon...

I dug up the first one last year and it had made it to 4.5 years, and I'm actually due to dig up the second one next week.