The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

This giant boulder is pinched over a 1000-meter abyss by two mountains.

A series of waterfalls so massive they straddle the border of Argentina and Brazil.

This stunning mass of ice spans 121 square miles and is still growing.

A set of ancient drawings in the desert of Peru that are so massive, many of them can only be fully seen from the sky.

The 953 windows undoubtedly make this the world's most beautiful screened porch.

This "preacher's pulpit" once used for pagan ritual, is home to a new, and dangerous ritual.

The central mosque of this Mali town is entirely built from mud.

Landscape of bizarrely shaped desert mountains and innumerable rock carvings.

An Ethiopian "Jerusalem" featuring a church hewn out of a single rock.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

These azure waters were thought to lead to the Mayan Underworld.

Walk 2,300 feet above the ground on the "Troll's Tongue."

Amsterdam's Red Light District leaves little to the imagination.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

A rare tour of an aristocrat's private home reveals valuable 17th-century paintings from artists like Rembrandt.

Amsterdam's former hotspot for public executions and dissections.

A collection of biblical memorabilia.

A public urinal so pretty, it was declared a national monument.

A unique collection of gilded age mechanical pianos.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

The world's oldest Jewish library was founded by Sephardic Jews in 17th century Amsterdam.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.