A flooded Mexican cave that hides a river beneath the water.

Rumored to be the famed pirate's lookout tower, this historic stone structure is now just watching for tourists.

This huge pile of volcanic boulders hides a stunning network of secret grottoes.

This popular tourist cave was ignored for almost 200 years before being mined into an attraction.

Come for the flowers, stay for the bats!

An ordinary pond with fish from out of this world.

The once highest point in China blends symbolic design with a kick of adrenaline.

Copenhagen's celebrated theme park and gardens.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Stalactites and stalagmites in a beautifully lit cave.

Museum celebrating the ocean, with the largest wunderkammer dedicated to sea exploration.

2300-year-old Roman road connecting the empire.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

A volcanic old faithful, Stromboli has been erupting continuously for the last 2000 years.

Thousands of well-dressed mummies below a monastery.

What once sat in the world’s spotlight is today a largely disused ghost complex.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

A "miracle" that seems to produce more holy fistfights than holy revelations.

The home of the Dead Sea Scrolls is an abstract modernist dream.

The loneliest plant in the world resides at the Durban Botanic Gardens...mostly.

Haven for Cape Fur Seals, until the Ring of Death of jumping Great White Sharks arrives.

The tallest bronze seated statue of the Buddha in Japan.