Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

Structure built from the skulls of vanquished foes.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

This endearingly discomfited urinating statue commemorates the sneaky pees had by us all.

A subterranean house of worship carved right out of the bedrock.

This mysterious but iconic tapered tower appears in many Azeri fairytales and legends.

The building's fluid, wavelike walls are a true feat of architectural ingenuity.

A shrine of fire worship built on top of a natural flame.

Resonant stone, that has been played since prehistoric times.

Home to nearly a third of the world's mud volcanoes, Azerbaijan is home to a messy, bubbling, and sometimes explosive landscape.

Mysterious hillside with a continuously burning natural fire.

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

This architecturally eclectic fortress witnessed centuries of bloody turmoil, including the massacre of its ruling clan.

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

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

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

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

Underground monastery and fortress.

340-foot statue built to honour the Heroes of the Soviet Union.

London's marvelous wildfowl reserve along the Thames.

An abandoned bell tower in the middle of nowhere is the last testimony of a forgotten medieval village.

A forgotten remnant of the Soviet Union, Transnistria is an unrecognized country hidden behind a heavily militarized border between Moldova and Ukraine.

Three small rooms at the back of the “official” church of London's clowns.

An artsy hidden staircase leads to breathtaking views of San Francisco.