About 4 years ago I had a day to kill in Detroit and went driving around the industrial "ghost town" of parts of Detroit. Fascinating, solemn, sad.
Not too far from the railroad station hotel I stumbled across an early 1800's coastal defense fort designed to keep those rabid barbarians from Canada out of the U.S.

The fort is now a city park along the Detroit River and it was overrun with kids playing organized soccer.
They are starting to restore some of the buildings and there are striking similarities to Ft McHenry in Baltimore, but a fascinating side story is that the museum of the Tuskeegee Airman is located in one of the restored military quarters. They have a lot of documents, photos, and stories there and a very knowledgeable tour guide. If you have any interest in military history it is well worth checking out.