The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

Villagers have recycled bomber fuel tanks from the Vietnam War and turned them into very, very strong boats.

A boat ride through utter darkness, lit only by headlamps, reveals an emerald green pool locals believe is sacred.

World's largest cave was only discovered in 1991, and now offers tours to the public.

This retro underwater observation tower would make the perfect lair for a sea-loving villain.

This beautiful and unmissable little museum is full of fascinating artifacts from Mesoamerica's great civilizations.

This unique medieval artwork featuring the story of the Antichrist remained lost for decades.

This medieval sanctuary's tree-framed door looks like a portal to a mythical realm.

A black cottonwood gets a second life as a home for books.

Three hundred illuminated pillars form an “artificial forest” in Medellín.

A lush indoor jungle fills this bustling Madrid transportation hub.

The walls and streets of the ancient city are peppered with penises.

The original resting place of Queen Cleopatra and Mark Antony's only daughter.

The fading, forgotten remains of a once bright and booming factory.

A uniquely lettered street sign marks the corner where the iconic word game was invented.

A star-shaped fortress town fort built in the geometric model of the Renaissance utopian city.

A galaxy of glowworms—larvae of a gnat—hides deep in the belly of these caves.

This magical space partly designed by Antoni Gaudi is one of the best examples of romantic gardening in the Mediterranean.

The oldest Jewish cemetery in Southeast Asia is a monument to a disappearing community.

The world's largest public collection of PEZ memorabilia.

The final resting place of American icon Buffalo Bill, and a museum that aids in telling his tale.

A stark reminder of the huge nuclear weapons plant that once stood on the site and its effect on the surrounding area.

Rather than a run-of-the-mill franchise hotel, this lodging has been decked out in dinosaur decor.