The hidden lair of an alchemist rediscovered in a 2002 flood.

Stalactites and stalagmites in a beautifully lit cave.

Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

An ethereal glowing blue ocean cave in Croatia.

The world's longest known cave system.

Amazing and mysterious Neolithic settlement on Scotland's Orkney Islands.

A battle between nature and architecture in the Cambodian jungle.

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

Hanging over one of Japan's "hidden valleys," these vine bridges must be remade every three years.

Iceland's largest lagoon is home to stunning multi-colored icebergs.

Take a drunken tour inside the world's largest known geode.

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

A seemingly endless landscape of pure salt stretches far across Bolivia.

Architectureal fantasy quarter of Rome.

Tubing through a cave lit with glowworms is a magical underground experience.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

Pompeii's less famous neighbor is still revealing her secrets.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.