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

Football field-sized microalgae production tanks on the Hawaiian coast create a stunning view from space.

A tunnel of hardened lava along Maui’s famous Road to Hana.

This unusual lava tube spouts seawater during high surf.

An ancient stone fortress considered by many to be the eighth wonder of the world.

An Aztec temple, the largest man-made pyramid in the world, sits buried in earth with a Spanish church set on top.

This curious fresh and salt water lake holds a secret that draws in deep divers from around the world.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Preserved Inca city and site of the last Inca stronghold against the Spanish conquistadors.

Unexplained bald patches in the landscape grow and recede over time, as though they are somehow alive.

This floating garden in the sky is straight out of a fairy tale, but the real thing is nothing short of magical.

An unfinished tomb carved into a giant boulder in the Arabian Desert.

Enormous sandstone towers loom within a Czech forest.

The southernmost outpost of the Russian Empire in colonial America.

This massive blockhead sculpture hides an entire library.

Flames have been burning within this mountain for more than 2,500 years.

This spectacular track has run continuously since 1882.

Traveling this mountain pass reveals quaint stone buildings, stunning Irish scenery, and a bridge said to grant wishes.

An alchemist's "magic door" stands in the middle of a Roman park.

Legend says this mysterious stone head belongs to a woman who was petrified by an alchemist.

Only a fragment of this 15th-century Dance of Death survives today.

Step into a cartoon at this Seoul café that aims to evoke a two-dimensional scene.

A hidey-hole sandwiched between cellphone, DVD, and jewelry stores features Tibetan delights.

The stoutest tree in the world.