This huge pile of volcanic boulders hides a stunning network of secret grottoes.

Iran's colorful terraces are a rare geological masterpiece.

This narrow canyon has been carved by the river over thousands of years into spectacular and curious forms.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

Exploring the wilder, more passionate sibling of Erg Chebbi feels like discovering a secret sun-kissed planet from another galaxy.

The only fixed chain and post trail in Scotland snakes its way along the base of a towering seaside cliff.

A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

This black shoreline is made up of exploded lava particles.

Earth's tallest volcano is sacred to Native Hawaiians, and home to a dozen world-class observatories.

Over 2,000 ancient temples dot the Myanmar landscape at the site of this famed archaeological site.

A precariously perched golden rock defies gravity and brings pilgrims from across Myanmar.

A remote candy-striped mountain in the Peruvian Andes straight out of the pages of Dr. Seuss.

Keshwa chaca, among the last handwoven Incan bridges, crosses Apurimac Canyon in Peru.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

This red lake 4,000 meters above sea level is home to rare flamingos.

A valley of unique erosion patterns lends to a view like nothing on Earth.

A seemingly endless landscape of pure salt stretches far across Bolivia.

An explosion of natural color known as "the river that ran away from paradise."

This whimsical stacked cabin looks like something out of a children's book.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.