A flooded Mexican cave that hides a river beneath the water.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.

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

Found down a long dirt road, a sacred Mexican cenote and 18th-century hacienda remain hidden.

A cenote filled with Colonial era artifacts whose waters cannot be accessed.

A limestone grotto where daylight filters in from below and turns the water a beautiful turquoise. Also home to a small underwater nativity scene.

This wooden mosque is one of the few remnants of medieval Poland's Muslim Tatar community in this deeply Catholic country.

A rare venue to buy specialty maps.

Poet Antonio Machado's former residence offers the quintessential Castilian lifestyle of the provincial towns in the early 20th century.

Hidden underground, a remarkable 10th-century bath complex survives virtually unaltered.

The first miniatures museum in Asia contains all sorts of itsy-bitsy wonders, including the world's smallest working television.

Local folklore claims that this wall was not built for defense, but to provide labor during a time of famine.

In this 400-year-old hotel in Madrid, you'll find a comb in every room, an old clock, and maybe a ghost.

This solitary convex mirror sculpture at an abandoned ferry station at the edge of a fjord reflects the scenery back at the viewer.

The second-largest giant sequoia in the world.

Remarkably intact Roman stone fortifications have encircled this Spanish city for centuries.

This humble bench is considered the most beautiful in the world.

This sculpture of a rhinoceros suspended above a city square is meant to evoke the weight of the human condition.

Visit a haunted Mughal mosque and the tomb of a Sufi saint and his disciple.

The story behind this beloved toy—named for Theodore Roosevelt and owned by his grandson—is more complicated than you might guess.

The 3,600-year-old archeological sensation is considered to be the oldest representation of the cosmos.

This is part of the Francke Foundation Museum, a curiosity cabinet filled with different scientific and natural wonders.

The National Park Service’s best-kept secret with views that rival any in D.C.

The cutest way to stay safe in traffic.