What's the longest amount of time you spent trying to find something?

As a child, the house we grew up in had a very large tree in our back yard. I had a memory of burying some skeleton keys near it but couldn't remember where. The house was old enough that we'd find skeleton keys occasionally and also as a kid they are special.

I searched for days, weeks, months... Digging holes all over the yard and under the tree. I recruited neighborhood kids and friends.

For two summers we searched for buried treasure. Never found them. Might have been a dream I had of burying the keys. I still think about it occasionally and wonder. The tree is long gone and the truth is I'll never know for sure.