Over the centuries, this island paradise has done it all, from providing monks with ecclesiastical respite to sheltering an exiled Leon Trotsky.

A marvel of Byzantine engineering under the streets of Istanbul.

Legend says if you stick your thumb in the hole and it gets wet your wish will be granted.

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

This shuttered power plant is now Turkey's first industrial archaeology museum.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.

In this breathtaking canyon, crocodiles bask on boulders and glide through the murky waters.

Clap your hands at the base of the pyramid, and the song of a sacred Mayan bird will echo through the air.

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

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

Norway's oldest cathedral still in use.

A monument to the thousands of Canadian soldiers who died capturing the French ridge during World War I.

The ruins of this gorgeous clifftop castle look like something from a fantasy novel.

Running under an entire mountain, the longest highway tunnel in North America is kept fresh using portal fans and jet fans.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

The facade of this relic from the Klondike gold rush is decorated with over 8,800 pieces of driftwood.

A historic freight system that found the true gold rush is in tourism.

A rare chance to get up close and personal with a 13-mile ribbon of ice near downtown Juneau.

Once a favorite playground for the world's most illustrious guests, Hotel Nacional's secret weapons and bunkers reveal a more menacing side to its golden history.

A focal point of the Cuban government, this city square features one of the most iconic images in the country.

One of Mexico's least-visited archaeological sites is tucked away inside a theme park.

An eclectic blend of esoteric imagery covers its interior.