A magnificent, glittering building tucked into a tiny Bulgarian mountain town.

Mysterious standing stone formations looks like a petrified forest.

The remarkably well-preserved final resting place of a powerful ancient Thracian king.

This once-grandiose behemoth of a monument from the socialist era now sits quiet and closed up.

Outstanding, eerie frescoes and decorations fill this 19th-century monastery.

A spectacular Bulgarian cave resembling a devil's head with a waterfall rushing down its throat.

The second-largest Jewish temple in Bulgaria was deserted after World War II, seized by the communist government and then abandoned again.

An ancient Thracian city where fire rituals were practiced on the largest cult altar in Southeast Europe.

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.

This massive concrete sculpture is said to be the heaviest communist monument on Earth.

Bizarrely shaped rock formations in northwest Bulgaria come with equally bizarre legends.

This little medieval church hidden in the center of Yerevan was lost and rediscovered—twice.

This 15th-century cave complex is one of the very few monasteries to stay open throughout World War II and the Soviet regime.

The “Sistine Chapel” of the Middle Ages merges 11th-century science and religion in wondrous hues.

An underwater restaurant, surrounded by a coral reef.

One man's personal kunstkammer, museum and shop.

A stunning landscape of bunkers that once stored chemical weapons.

This network of conjoined cellars was riddled with traps and supposedly allowed the townspeople to pretend their homes were deserted.

A maze of underground tunnels beneath one of the most beautiful forts in Serbia.

Featuring a casually threatening atmosphere along with dessert and coffee to die for.

A beautiful 62-acre Catholic shrine and botanical garden.

This garden is dedicated to a Portland cartoonist who specialized in dark humor.

Portland had a unique approach to Cold War-era protections.

The U.S. Navy's last diesel-electric submarine rests half-submerged in the middle of Portland.