At the Arizona-Nevada Border in the southwestern United States, the Hoover Dam has been standing tall since 1936. Originally called the Boulder Dam, this hydroelectric power station held the title of "world's largest" until 1945 with the completion of the Grand Coulee Dam. It was declared a national historic landmark in 1985.

Photo Credit: Ken Lund, 2010 - taken with a Canon PowerShot A540 - and used via a Creative Commons license.