Daveydude mentioned this event cache to me today
They give you a passport and you visit spots around town. It sounds like lots of fun and unless I-5 is closed by snow I'll try to attend.
They had something a lot like this in Salt Lake City for Geocoinfest (which I thought about attending but ended up in Las Vegas instead.) They hid caches along the light rail line and you had a passport to complete.
Last year I planned to do something a lot like this. I bought a bunch of rubber stamps to prepare a "Southern Oregon Passport" series. I think the main reason I didn't complete it was because I was torn between making the caches difficult (nothing I hide is very hard, but I'm talking "hiking required") or making the caches easy so that more people would find it. I still have the stamps and containers so maybe this will still happen.