Roman ruins, natural methane fires and a lovely beach.

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

Flames have been burning within this mountain for more than 2,500 years.

This eatery re-creates dishes from the Ottoman Empire so you can dine like a sultan.

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

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

A small etching on the white marble parapet was written in runic script by a Viking mercenary.

The ornate miniature mansions were built for Istanbul's feathered residents.

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

A marvel of Byzantine engineering under the streets of Istanbul.

Launched by Napoleon's soldiers more than 200 years ago, a cannonball remains embedded in the tower wall.

Also known as the Blue Church, the building was consecrated to the daughter of Andrew II.

Thousands of slain Soviet soldiers are buried within the shadow of this enormous obelisk.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

A neo-Gothic church built to thank God for saving the Emperor of Austria from an assassination.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

A silly medieval mural preserved on the side of a Viennese house.

Legends surround an ancient tree trunk riddled with nails for good luck.

A spherical "micro-nation" in the heart of Vienna.

The final resting place for the remains of 143 Habsburg royalty.

Bohol's mysterious brown hills.

A patch of Philippines forest devoted to saving the lives of an emotionally sensitive species of googly-eyed primates.