We had no idea that Indiana had 150+ foot tall sand dunes that you could hike and roll down, but boy do they.  We spent a few hours at the Lake Michigan beach just playing in the sand, throwing rocks, and learning to be good polar bears.  The water is freezing!
We scaled Mt. Baldy, the largest sand dune we have ever seen, and rolled down in fine fashion from the top – put all of this in a loop that repeats about 10 times and you have it.  The place was really cool with lots of rocks, sticks, and dirt – the things boys like best.