A marvel of Byzantine engineering under the streets of Istanbul.

A full figure 4th century incorruptible saint lies in a glass coffin in Croatia.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.

This Roman monument is surrounded by more recent construction, offering a stark contrast between ancient architecture and the modern urban landscape.

At this unique farm, you can interact with adorable donkeys and view an ancient dolmen.

The bones of this aquatic dinosaur turned to opal over the centuries and the beast's remains were almost sold as jewelry.

A cluster of historic bathhouses built on the famed hot springs that gave the Georgian capital its name.

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

A gargantuan crystal kingdom.

A winding, blood-red tunnel of hardened lava navigable by foot.

This volcanic cave lake is essentially hard proof that Iceland is the most magical place on Earth.

Beneath Denmark's Højbro bridge, a bronze merman and his seven sons forever mourn for the mother and wife who left them for land.

Iron Age "bog person" preserved for over 2,300 years.

This colorful artistic feature atop a Danish art gallery allows visitors to stroll through a rainbow.

A 19th-century subterranean reservoir repurposed as a contemporary art cave.

An ultra-modern diversity park in Denmark has turned an entire city block electric pink.