This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

The crumbling ruins of an abandoned 12th-century monastery.

One of the few places in Portugal where the Celtic ritual of wearing large wooden masks is still practiced.

This architectural beauty is the home to a personal collection of more than 600 examples of mechanical musical instruments.

This museum contains a vast array of puppets and marionettes from all over the world, featuring incredible works by Portuguese creators.

An abandoned tuberculosis hospital said to be haunted by the patients who died within its walls.

A small but charming botanical garden that contains many exotic plant species.

This crumbling Portuguese ruin overlooks the populace it once ruled.

Building owners can take out tiles for free at this repository for historic building materials.

This unassuming chapel in Portugal plays host to a ghoulish collection of bones.

"Portugal's Stonehenge" is made up of nut-like stones aligned with the heavens.

This abandoned five-star hotel is now a five-star urban exploration destination.

An abandoned mine now resembles a post-apocalyptic landscape of derelict buildings and blood-red pools of water.

Picturesque intersection of witchcraft and ancient Christianity.

The verdant mossy ruins of a Franciscan monastery lie in the remote Sintra hills awaiting exploration.

Perhaps the most spectacular grotto along the Algarve coastline.

A submerged village appears when dam levels drop.

This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

This small chapel is built of human bones and decorated with a golden skeleton.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

This charming candle shop has been in business since 1789.

This subterranean passage reveals the city's mining history as well as its legendary terrors.

The spectacular subterranean collection includes dazzling minerals, including a piece of "kryptonite."