Just south of Avenue P on the west side of Brooklyn’s Ocean Parkway, a small, one-foot-tall granite rectangle juts out of the ground with a mysterious “3M” carved into its traffic-facing side. This inconspicuous stone was once a mile marker on Ocean Parkway, a street inspired by the grand boulevards of Paris and Berlin, built between 1874 and 1880 in the middle of Brooklyn, New York. Originally, Ocean Parkway was a shortcut for pedestrian and horse traffic, as well as strollers and carriages, to Coney Island Beach from Prospect Park….
