The seawater playground of gilded-era San Francisco burned to the ground in 1966.

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

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

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

This neon lit Georgian cave claims to hold the boulder Prometheus was chained to.

Unusual building appears to be haphazardly built from randomly piled bricks.

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

Fortified homes of highland warriors that are still in use today.

Underground monastery and fortress.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

This famous city eluded concrete detection until the early 2000's.

A marvel of Byzantine engineering under the streets of Istanbul.

Roman ruins top white travertine terraces formed by ancient hot springs.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A huge musical instrument played by the ocean.

Underwater art project will double as a massive artificial coral reef to help regenerate the damaged ecosystem.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Every equinox this Maya pyramid puts on a spooky ancient light show.

Colorful boxes placed over the dead are left to rot and crumble.

A trading post in the North Pole where children send letters.

The king of U.S. high points towers over every other peak on the continent.