The slight bump with darker grass, towards the right of this picture, is the top of the "Sleeping Bear Dune" for which the park is named. (Here is the Ojibwa legend which gives the dune its name.) It was more impressive a few hundred years ago, but dunes are built up and torn down relatively quickly by erosion. Older pictures of the dune, along with a slightly different version of the legend, can be found here.
In the distance are the Manitou Islands.