MADAWASKA, Maine — A 69-year-old Waterville man just landed in Madawaska, completing his three-year-long project of walking all four corners of Maine — a total of 660 miles. Madawaska marks one of the four corners of the United States along with San Ysidro, California; Blaine, Washington; and Key West, Florida. Visiting all of them is a popular motorcyclist quest, and those who reach each corner find a designated park or landmark that lets them know they have succeeded. Madawaska also marks one of the four corners of Maine, along with Lubec Post Office, Kittery Trading Post and Grafton Notch State Park.