As you travel down from upper Michigan, all along Lake Michigan are state parks and beaches with some of the greatest beaches and sand dunes you will ever see.
In order to dip your toe into the fourth great lake, Lake Erie, you must go to the southeast side of Michigan just south of Detroit. If you take this trip, the Henry Ford Museum is a must see.
If you hug Lake Michigan all the way to Indiana, there are a couple a stops for the kids, Michigan's Adventure near Muskegon and if you are into World War II ships, also in Muskegon is the USS Silversides near the Great Lakes Naval Museum.
If you like beaches that are not widely traveled, then in Fennville, Michigan, there is a public beach at West Side Park that is a must stop. This beach is mainly pebbles along the shoreline, with a nice sandy area to sit on and a sandbar about 50 yards out in the water.
Farther down is Holland, Michigan which has a tulip festival every year, Benton Harbor, and my favorite beach in Michigan, the Warren Dunes.