i did a pirate treasure hunt a few years ago for a family reunion......
get your self a cheapo styrofoam cooler and then proceed to color (markers, crayons, paint.....) it brown or black. decorate it with a skull and cross bones(get creative and draw it or get one from clip art online and print it large, cut it out and paste it on.)
fill it with any sort of "pirate goodies" that your family would enjoy. (we did candy and toys from the dollar store) while the kids are off occupied with something else, hide the chest somewhere. if it is in a very public place, you may have to have someone casually stay near the chest to make sure no one else gets it. We tend to hide it somewhere near/at out own site and the clues below take them all over the place but ending them back at our own site.
then create clues to take them on a wild goose chase. on clue leads to a small flag where the other clue is hidden. that clue leads them to a small flag (just a fabric stip or a piece of ribbon) where another clue is hidden....and so on until the last clue found leads them to the treasure chest.
i tried to make my clues ryme or put a story to the clues....like: "legend tells of the tale of a ruthless pirate black beard. His men said he was the lowest of the low. the first clue to his treasure is marked with a blue flag and is as low as a snakes belly" OR "on the old oak tree, on branch number two, you will find a blue flag that will be your first clue."
that kept them running around the park for about an hour.