World's largest cave was only discovered in 1991, and now offers tours to the public.

A centuries-old forgotten underworld lies beneath Malta.

This stunning natural double arch, the largest in the Alps, went undiscovered until 2005.

A one-of-a-kind collection of a unique medium.

An exquisite tunnel of cascading flowers.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Italian poet Dante Alighieri is entombed in this small mausoleum in Ravenna, and his hometown of Florence has never been too happy about it.

This former quarry is now a picturesque gorge that hides a sunken lake.

Ruins of a German Castle on top of a towering stone pillar.

The only university zoological museum in London houses extinct animals, bizarre natural history specimens, and a Micrarium of microscopic creatures.

A sprawling Baroque park with 300-year-old hydro-pneumatic waterworks.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

Centuries-old bridges grown from tangled roots.

Experience park where visitors are told to expect the unexpected.

The longest hedge maze in the world.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

A haunting collection of the vanished and disappearing natural world.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

Stalactites and stalagmites in a beautifully lit cave.

The most visited, and possibly most controversial, museum in Germany.

The most iconic structure in Scotland has been home to bishops, colonels, and Sean Connery characters.

This massive library holds what was once the largest book collection in the world.

Paris' linguistic guide to the international language of, yes, love.

A gargantuan crystal kingdom.