Can anyone suggest cool sightseeing spots near Lake St Clair or Lake Huron? I'm not sure if Metro Beach is open in the winter for free sightseeing. Back on the east coast, the public maintained beaches are "open" in the winter (for free) but there are no lifeguards so you're not supposed to swim. I'm just looking for a place to check out the lakes without having to pay.

Metro Beach should be open.
There are parks in Lexington and Lakeport along Lake Huron.
There is a ferry to Harsons Island, Russel Island and Walpole in the St Clair River.
Pinegrove Park under the Blue Water Bridge in Port Huron is a nice view of Lake Huron entering St Clair River.
The public beach in Marine City (very tiny) is the closest point that the freighters pass land in the entire Great Lakes system.
If you're in Marine City you should stop at Gar's for what may be the best cheeseburger you'll find anywhere.

Lighthouses!

I'm not sure what is open but there is a lot of nautical history in Michigan's lighthouses. In my youth, I woke up the the fog horn on the Lightship Huron on many mornings.

Fred