The discovery was made on July 24, 2007 during an underwater exploration on a remote tributary in the upper Mississippi River basin in northern Wisconsin. Unlikely as it sounds, the site appears to be an ancient underwater structure -- possibly a road or causeway -- constructed of flat, rectangular-shaped blocks of stone that appear to be cut or otherwise worked and then carefully fitted into place. Although likely of natural origin, to the casual eye the "structure" looks amazingly like ancient stone-paved roads or other ruins found in MesoAmerica, Europe, and elsewhere.