An engineering and historic marvel. Just be careful of the U.S. Dept. of the Interior wanna-be Police. Did a y-turn at entrance of "staff parking" lot and was accosted and threatened by one of these macho jerks. Was completing five days of travel throughout southwest (including Yosemite, Las Vegas, and several small towns), and the worst treatment I received was at the hands of a U.S. government employee.