A Texas cave network is home to some of the world's most spectacular-looking and bizarrely named mineral formations.

This concrete tangle of square pipes has stood as a proud thorn in the city's side since the '70s.

The longest continuous lava tube in Oregon.

The perfectly named cave drop is the deepest in the continental United States, almost matching the height of Seattle’s Space Needle.

Abandoned silver mine strewn with wrecked and twisted structures.

One of the last free public hot springs is decorated with hippie art.

These sub-farmland caves are home to a majestic stalactite known as the "Crystal King."

Mile-long cave system near Great Smoky Mountains.

America's only nuclear missile silo open to the public.

The artist James Turrell is repurposing an extinct volcano crater as an observatory to experience the cosmos.

This painted blacktop brings the classic arcade game to life.

A medieval castle in the middle of rural Texas.

Half of a waterfall goes into the river while the other half seems to disappear.

These Great Lakes sea caves accessible by boat in the summer turn into temples of ice reachable by foot in the winter.

Constant erosion has created a surreal landscape of bleached and preserved fallen trees.

A hidden beach at the end of a tunnel of mangrove trees.

Treehouse motel and treehouse-building school.

This large midwestern cavern features impressive rock formations and an underground waterfall.

Giant origami sculptures tucked into desert scenery beckon passers-by to explore further.

This naturally heated mountainous creek has created a group of neon blue pools of potentially deadly boiling water.

This ancient sinkhole-turned-healing-pool is a treasure trove of archeological discoveries and may even be the Fountain of Youth.

The "world's biggest dinosaur" once housed a creationist museum in its abdomen.

An underground magnet for ever-changing street art.

The flower-shaped temple in Virginia aims to transcend the boundaries of the world’s religions.