This lake in northwest Iran has started turning from green to red more frequently than scientists are comfortable with.

This beautiful system of tunnels built into natural rock serves as a centuries old plumbing system.

Iran's colorful terraces are a rare geological masterpiece.

Modern-day cave dwellers carve elaborate homes out of volcanic debris.

Some call this eerie forest of crooked trees the "Bermuda Triangle of Romania."

This Romanian village may have been drowned, but it is long from forgotten.

17th century mosque for Shah Abbas' harem.

This exceptionally well-preserved ancient marvel also houses a small museum dedicated to Jordanian folk tradition.

This vast, water-filled underground labyrinth can only be toured by boat.

Ancient structures used to make and preserve ice in the deserts of Persia.

The tower in this 1,000-year-old mud-brick village seems to vibrate for no apparent reason.

The hottest, driest, and most scenic desert on Earth.

This ancient burial site is believed to be one of the first earthquake-protected structures in the world.

The ancient necropolis houses the immense rock-cut tombs of four Persian kings.

A whimsical bridge adorned with decorative dragons.

A miniature train-ride through Slovenia's largest cave system.

Tucked away in a small German apartment is an eclectic museum devoted to West African vodun culture.

The final resting place for the remains of 143 Habsburg royalty.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

This man-made mound monument was built out of soil from all across the Polish empire.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.