Actually, a fountain at the botanical gardens last week, with a few olives floating in it from a nearby tree.
They sink down and then slowly come back up. Tricky for little fingers to grab, but so worth the effort.
Who could have guessed that fishing these olives out and tossing them in a fountain over and over again would be the most fun thing we did this week? (And I'm not saying it wasn't a fun week, just that this olive game was really loved by one little boy)