Holy Hindu shrine in an enormous, monkey-filled limestone cavern.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

This Stockholm light tower can be controlled by anyone with a smartphone.

One of the capital's last independent milk bars remains a crucial community watering hole.

This tunnel entrance is built to resemble a grand castle but no one is quite sure why.

Magnificent Roman ruins lie vulnerable to destruction on the edge of the Mediterranean.

The largest greenhouse in the world is home to over one million types of plants.

This triumphal arch is the only fully standing structure that remains from Roman-era Oea.

A fortress-like granary that has been continually in use for more than nine centuries.

A beautiful oasis town dating back to the Roman period still serves as reprieve from the brutal summer sun in Libya.

70 years of foreign military influence on the shores of Tripoli, Libya.

The ancient heart of Tunis is an enormous maze of narrow streets and alleyways.

Some believe this abandoned Brutalist masterpiece inspired George Lucas's Sandcrawler.

Roman-era ships unearthed...

Ancient ruins hidden underneath a modern luxury hotel.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

A secret hatch containing two parchments was discovered in this statue over 40 years after its installation.

A secret climbing tree hides along the side of a Costa Rican road.

In Costa Rica's cloud forest, the roots of a woody ficus create a botanical bridge.

This World War II airfield is the last place the bandleader performed before he disappeared.

This group of small islands on Lake Nicaragua formed after an eruption of the Mombacho volcano.

The crumbling remains of a once-grand building.

This staircase full of Mayan hieroglyphics is perhaps the largest single text in the world.

A full-size replica of this well-preserved temple lets you take a walk through the Mayan age.