This whimsical seashell-shaped place of worship was designed to blend into its surroundings.

The world's longest tunnel with an undersea section.

This bridge's unique architecture honors nautical heritage and encourages self-awareness.

The remains of a centuries-old water system that inspired local legends of secret tunnels.

These markers are used to determine the ground stability of the Strip.

A massive marble foot is tucked away in a small alley near the Pantheon.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

Plaques on its facade commemorate the Tiber's most destructive deluges.

A deep mark on the remains of a Roman temple, believed to be left by a legendary warrior.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

This school was designed to support the rebuilding of African American schools around Delaware.

This heritage rail line meanders through Delaware’s Red Clay Valley.

The tombstone of the founder of the lost town of Ogletown is now stuck inside a traffic median.

A rural colonial settlement that contains the remains of a store and cooper.

The first marker along the famous boundary.

The meeting of the northwestern corner of Delaware, the northeastern corner of Maryland, and the southern edge of Pennsylvania.

A mosaic map made of over 100,000 tiles depicts the geological features and sea creatures that live along this San Diego beachside community.

A large sculptural artwork and garden in Escondido, California.

Sojourn to the past at this residence teeming with 1950s memorabilia.

The overgrown ruins of a once thriving World War I-era copper mine.

This dark, quiet forest on the outskirts of San Diego is dense with rumor and lore.

One poet's handmade, anachronistic home.

For almost 100 years, this site of peace and spirituality has existed on the California coast.

This cabin from the 1850s is one of the first structures built by Chinese immigrants in California.