In July of 1974 an aerial photograph of part of Sleeping Bear Dunes showed a man-made structure near Platte Point, where the Platte River meets Lake Michigan.The mystery structure may be a wall or "groin", which is a wall put up to deal with beach erosion. But nobody working at the park knows or remembers what it might have been. According to MLive.com, there's no record anywhere of this structure.

Soon, the Sleeping Bear Dunes wall may join Machu Picchu, Stonhenge and the Sphinx as one of the most mysterious places in the world.

Or not.

Could be just a wall of beer cans filled with sand. Anyway, if you were hanging around Sleeping Bear Dunes in the summer of '74 (and still remember it) help the Sleeping Bear Dunes Park staff out and call or email them.

Especially if it was you who put up that beer can wall. Here's the story.