Underground monastery and fortress.

Called the "Armenian Stonehenge," this ring of menhirs pierced with holes may be a prehistoric astronomical observatory.

Nestled in a peaceful valley, this Armenian monastery may have been saved from Mongols thanks to the eyes of God.

This Armenian monastery was carved out of cliffs and named after the spear used to stab Jesus.

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

Right up until the 20th century this network of man-made caves was the biggest village in Eastern Armenia.

A geological oddity topped with a 2,000-year-old pagan temple.

The oldest housing complex in Riga is a mini timeline of architectural trends.

The ancient water tanks remain some of the ruined city’s most beautiful architecture.

This picturesque medieval monastery guards a small trove of historic treasures.

Hundreds of unusual wheel crosses poke above the earth in this small Estonian cemetery.

Take a hidden path to the mouth of the cave to watch millions of bats swarm at sunset.

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

Amsterdam's former hotspot for public executions and dissections.

The oldest Jewish cemetery in Southeast Asia is a monument to a disappearing community.

A galaxy of glowworms—larvae of a gnat—hides deep in the belly of these caves.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

This large sand dune in the Netherlands is home to wind-whipped trees with "floating" roots.

After a profound show of devotion for his master, a dog becomes the symbol of loyalty for an entire nation.

A 70-foot-deep ice cave formed by lava from Mt. Fuji on the edge of Japan's "Suicide Forest." 

A boat ride through utter darkness, lit only by headlamps, reveals an emerald green pool locals believe is sacred.

A series of tiny artificial islands rich with produce bob atop the surface of the lake.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

The oldest family-run luncheonette in New York, last renovated in 1948, still serves food and drinks the old-fashioned way.