The ruins of an 11th-century Norman castle with a rare, perfectly circular shape.

The largest greenhouse in the world is home to over one million types of plants.

The excellent acoustics of this natural amphitheater made it a popular preaching spot for the founder of the Methodist Church.

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

Ring the bell to enter a bar that looks equal parts museum and old curiosity shop.

This unique architectural wonder is also tied to one of the 20th-century's most renowned writers.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

A collection of incredible clay crafts, complete with earthen skeletons and mermaids.

The largest collection of artifacts from the Olmec civilization, the mother culture of Mesoamerica.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

One of New York's best collections of pinball is hidden in a secret bar in the back of this laundromat.

A living archive of urban activism and space reclaimed.

More gold than anywhere else, ever.

“Invented in Key West, Perfected in Brooklyn."

The fanciest public restroom in New York City boasts fresh flowers, art, and a classical music soundtrack.

The factory for the popular Dumbo location, the Greenpoint shop is a quiet gem.

Curious crustaceans support an obelisk from ancient Egypt that now stands in modern-day Central Park.

A hidden architectural treasure in New York's Brooklyn.

Ride the subways of yesteryear.

The one-stop shop for all of your superhero (or evil arch-nemesis) needs.

A decommissioned military complex that's now a modern industrial park.

This striking arch, one of the first architectural elements constructed in Prospect Park, was recently restored to its original glory.

An arcade packed with a rotating collection of unique independent video games.