A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

Retirement home for giant obsolete machines.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A fascinating insight into daily life in the Eastern Bloc.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

Immortal combat in a Moscow museum.

The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

A dormant lightning machine equal to all the power in Russia.

The world's oldest map of the holy land gives us a fragmented glimpse of the layout of biblical nations.

A marvel of Byzantine engineering under the streets of Istanbul.

A 250-year-old timepiece-automaton adorned with golden mechanical birds, which still sing to this day.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

These ominous lava formations were said to be an entrance to the netherworld so of course they inspired a famous metal band.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

Man-made mineral caves house massive bat colony.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

This elaborate temple was built around one of the Buddha's teeth.

Once thought to be the Garden of Eden it holds a holy footprint claimed to belong to Adam, Buddha and Shiva.

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

The charmingly disheveled clock tower of Tbilisi's puppet theater.

A cylinder monument with a spectacular vista commemorates a friendship that some say never existed.

A museum glorifying the life of Stalin, located in the city of his birth.

Take respite inside this jaw-dropping church while climbing the volcano where Georgia's Prometheus was once chained.

The most visited pilgrimage site in Armenia once held a saint in a pit for 13 years.