A Norwegian-born sculptor created these soaring guardian angels at the entrance to Hoover Dam.

Experience a charming 1930's version of "infotainment."

The site of the gruesome massacre—and maybe cannibalism—of five men, a tragedy that made Alferd Packer infamous.

One of the oldest active carousels in the country—but it might be missed by all but the keenest-eyed boardwalk strollers.

Although built to generate electricity for Marylanders, this dam has become an all-you-can-eat buffet for American bald eagles.

A unique museum where guests can rent and operate a locomotive.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

One of the oldest standing structures in Montgomery County, Maryland.

I-95's Tijuana-style celebration of kitsch at the Carolina border.

One of the world’s largest collections of petroglyphs records 2,000 years of human activity.

A walk through the historic city center, under the streets of Seattle.

During World War II, blimps were a key part of the United States' defense against German U-boats—this building could house a dozen of the armed airships.

Home to the largest urban bat colony in North America, estimated at 1.5 million bats.

Native Americans built this circle of stones, which was used to predict astronomical events.

California's first suspension bridge.

A showcase of engineering might that was also symbolic of westward expansion.

This ancient market is often referred to as the oldest shopping mall in the world.

The hallucinogenic center of the ancient world.

The remnants of a wooden-hulled fleet built and abandoned in WWI, now home to a thriving ecosystem.

This advertisement for talcum powder was painted on the rock face and has since defied removal.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

This innocent-looking townhome is actually a subway exit.

The final resting place of the businessman-turned-astronomer who helped discover Pluto stands near his observatory.

The only structure left with direct ties to the Salem witchcraft trials of 1692.