There was a group on southbayriders.com that had a little home made medallion that was put somewhere in the area. It had to be within 50 miles of San Jose. You proved you were the first one there by getting the medallion and leaving a note indicating that whoever else found the place was too late. You were supposed to post as soon as possible that you found it. You then had a few days to hide it somewhere else and post your hint.
I followed that one for quite a while and knew many of the places. I even left work in the middle of the day once to try to go find it, but all I found was the note indicating that I was too late. People who don't have to work daily usually did a lot better than the rest of us.
Anyway, you might consider including a physical object as part of this.
__Scott R. Nelson, 2008 KTM 990 Adventure, 2001 Honda XR650L, Folsom, CA