The Indiana Dunes has 2,182 acres of "primitive, beautiful, historic and unique Hoosier landscape." The State Park has three miles of shoreline with Lake Michigan, making it a popular summer beach spot. The sand dunes are incredibly tall--over 200 feet--which makes for pretty views over Lake Michigan as well as over the state park.

There is a fee for admittance. 

Website: http://www.in.gov/dnr/parklake/2980.htm