I really love scavenger hunts, egg hunts and treasure hunts.
I have a memory of an Easter hunt when I was 5, but no-one else seems to remember so it might have been a dream... anyway, the memory is about searching the home for my "easter egg", which was a page of tiny paperdolls.
One thing I liked about Dan Brown's Da Vinci Code was the coded treasure hunt...
"Richard G. brown, Dan's father, put together many types of treasure hunts for the kids when they were young that were challenging, yet fun. His dad would map out this treasure hunt carefully, and the kids had to unlock codes to find their Christmas gifts for example."