The world's longest tunnel with an undersea section.

Not far from the more famous House of Juliet, visitors will find the supposed residence of her lover.

Pilgrimage site for star-crossed lovers.

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.

This underground church is topped with a 500-foot cross that is seen by many as a beacon of fascist hubris.

This magnificent castle grew from a small Moorish fortress, and reportedly inspired two iconic Disney castles.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

A tribute to the statues of Easter Island along Route 66.

These markers are used to document elevation changes around the famed dam.

An old railroad grade built for the construction of Hoover Dam is now a recreational trail featuring several tunnels and sweeping views of Lake Mead.

One of the world's tallest Ferris wheels takes visitors high above Las Vegas in a spinning party room.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

Brightly colored 30-foot-tall totems light up the desert sky just outside Las Vegas.

This museum devoted to the gothic author holds such interesting ephemera as his socks and walking stick.

Rare recess caves fill this unbelievably beautiful Ohio park.

Welcome to old Florida, where a 1940s mermaid show is still enchanting visitors.

The largest earthwork effigy in the world.

One person's lost luggage is another person's treasure.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

The world's longest known cave system.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A beautiful geyser under environmental threat.