The largest and best-preserved rotunda in Prague.

Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

Prowl through this sprawling bazaar under a massive Soviet-era dome for delicious eats.

Once a luxurious flagship of the Soviet Union, this Brutalist structure remains a landmark of Tashkent’s communist past.

An underground world of gorgeous, palatial metro stations designed as a nuclear shelter complex.

Controversially restored in the 1970s, this giant 15th-century mosque is shrouded in legend.

The Avenue of Mausolea is a series of grand palatial tombs.

An 18-meter-long sarcophagus of a constantly growing dead prophet.

Light still pours into the ruins of this ancient Islamic observatory.

Home to what was once considered the largest gate in central Asia.

This "tower of death" has acted as an observatory, a religious hub, and an executioner's lair.

Ancient barriers wrap around what was once an important stop along the Silk Road.

These "50 Fortresses" have been unearthed in the ancient oasis of Khwarezm.

The ruins of an ancient Zoroastrian Tower of Silence believed to be the earliest example of the traditional funerary practice.

Once a bustling fishing port, this semi-ghost town is now more than 90 miles away from the shore.

Ancient serpentine sacrifice holder that has stood the test of time.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

Explore the frozen river and take a walk to a nearby island on some of the longest ice roads in Sweden.

The world's first purpose-built indoor shopping mall opened in Sweden in 1955.

A medieval village, with red wooden cottages around a stone church, stands as a well-preserved example of a settlement type that was once common in northern Sweden.

The world's first ice hotel is still one of the most elaborate and beautiful.

A design by master architect Alvar Aalto in a small village in the Apennines near Bologna.

This huge metal monument is slowly being stripped to its concrete skeleton.