One of the days while Grandma was here, we did a treasure hunt with Natalie. While she was napping, I took pictures of various places in our backyard, and I packed up little trinkets (stickers, small toys, a few pieces of candy, etc.) with the pictures. The pictures were "clues" to where she would find the next treasure and the next clue.
I wasn't sure if Natalie would understand the game, but she got it right away, and she was sooo into it: