Some of the tallest ancient American ruins continue to inspire awe and curiosity.

Inside this garden, visitors are offered a glimpse into how inhabitants of the region survived centuries ago.

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

The narrow passages will challenge even the bravest driver.

This pseudo-steampunk weapons facility is the world's largest wood and glue structure, and packs quite a wallop.

The remains of this early 20th century refinery loom on a mountainside like a graffiti-covered fortress.

The history of sea-faring refuse and disaster is on cramped display in this Netherlands folk museum.

This steel frame is a skeletal mirage of a lost 16th-century stone building.

This medieval castle was painted pink as part of a now-abandoned children's theme park.

This imposing tower named after the mythical sword of King Arthur is considered the tallest freestanding climbing wall in the world.

The ruins of a medieval castle that once belonged to one of the most powerful families in the Netherlands.

A true Valhalla for cactus and succulent lovers.

Hidden within a Netherlands crater is a stone bed that lets those who lie in it see the sky as a curved surface.

This impressive collection of rare books on ancient mysticism inspired author Dan Brown.

A beautiful maze marks where three countries meet.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

A sculpture for the sun and stars, created by Nancy Holt.

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.

This geothermal hot spring hides beneath a slowly growing mineral dome.

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

This rugged area of red rocks and arches is often considered one of the most beautiful places on Earth.

Bizarre lunar-like landscape with thousands of large stone "hoodoos."

One of the world's oldest and most massive living organisms is a grove of quaking aspens.