Located about 40 mi/64 km northwest of South Bend, Indiana Dunes State Park is on the shore of Lake Michigan.
If you want to climb the huge sand dunes, take along a pair of sneakers: The sand is often too hot for bare feet. (Be aware that small areas of the dunes have been fenced off for erosion control.)
You can also go for a swim, but remember that the cold temperature of Lake Michigan can take some getting used to, even in the heat of summer.
There are cabins along the lake for rental, as well as a number of activities and facilities—camping, cross-country skiing, a nature center and a wildlife observation tower.