My family went on a hike at Silver Falls state park recently, along the family of my sister's best friend when she was 10 years old, who happen to live in Oregon near where we were for Christmas.
The falls are quite spectacular. The river runs over a large volcanic slab, and the water has eaten out underneath the slab over time, so there's a ledge underneath the volcanic slab. A trail runs down underneath the slab and all the way around and behind the waterfall. I wish I'd remembered to bring my camera.