One of the sights at Indiana Dunes National Lakeshore that you can only see in winter is the "shelf ice" that Lake Michigan sends to shore.
These rafts of ice are pushed ashore by north winds. Because of the 300-mile length of Lake Michigan, there is a lot of impact to the south shore when the winds -- which can create waves 25 feet tall -- are from the north.
The floating ice is pushed against the shore and piles up, sometimes more than 20 feet high. By March, it will often be a half-mile or more in width. Walking on the ice is dangerous and prohibited by park regulations.
Visitors are encouraged to visit the lakeshore in winter to see these shelves of ice and the piles that are created when the winds blow the ice ashore. Since it does not occur at any other locations on the lake, it is one of the winter attractions of the park.