The event direction that I went along with was a theme of bird watching, but with a twist. The birds are the ones searching (with the children), so it is instead called "sculpture spotting."
Birds would direct you on the map towards the highlighted sculptures, and then once the kid discovers them, is rewarded with a card with information about the sculpture on it.
A couple of map variations, one with bird tracks and the other with a bird narrating the journey. I also played with different ways of indicating the sculptures on the maps, like with nests with eggs (a little too eastery though) or drawn icons of the sculptures.
And here were my rough (very, very rough) ideas for the birds that they would receive. I'm not sure if I want them to be trading cards or something that you can cut out and put in the craft tree that the kids have the option of making at the event. If they are trading cards, then after the event the become a little useless. If they're pieces for the tree though, it will last once they take the tree home, but what if they don't make a tree? Questions, questions.