Hoover Dam, of course, is a famous technological megaproject from the 1930s, spanning the Colorado River between Nevada and Arizona.  At the time, the railroad was the only practical transportation technology for such a large project, so a dedicated rail line was constructed to the dam site.

The upper rail line, which ran nearly to the top of the dam, got some desultory use after the dam’s completion, but the tracks were torn up after the last generator was installed in 1961. For decades, the old right-of-way just sat, blocked off with fences and “No Trespassing” signs.

However, it has since been repurposed as a recreational trail. The trail offers expansive views of Lake Mead and traverses several tunnels, and ends at the Visitor Center on the Nevada side. The trail is also open to bicycles and leashed dogs.