This imposing memorial contains the remains of Che Guevara — and 29 other guerrillas who died with him in Bolivia.

A 20th-century picture show in 3-D.

An ancient capital city that dates back 3,000 years old and harbors many surprises.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

This semi-secret storybook hedge maze is also the oldest garden in the city.

A temple to modernity, tucked away amid Barcelona's more well known museums.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

Deliberately hidden for centuries, the magnificent Saadian Tombs were eventually uncovered in 1917.

These crevices cut into the mountains collect the island’s main source of precious freshwater.

These wooden balconies that are both decorative and functional.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

A completely underwater art museum sends a stark message about humans' impact on the environment.

This Canary island is a quintessential example of nature’s beauty, and its unbridled fury.

An open-air museum showing how people on El Hierro lived from the time of the first settlers until the late 20th century.

Several petroglyphs are all that remain of an ancient pyramid.

The four landings commemorate a royal visit to Europe's biggest observatory.

A statue commemorating the island's tradition of dancing dwarves in Napoleon hats.

Volcanic rocks ground down into sand make this Spanish beach as black as night.

Hundreds of caves once used to store grains and animal feed.

This laboratory has a remarkable concrete roof that measures less than an inch at its thickest point.

Located in a veterinary school, this macabre exhibit displays the effects of animal diseases.