Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

Tucked in the back of a flower shop, its collection details the fascinating history of the Netherlands's iconic symbol.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

This museum housed in a former brothel explores the past and present of sex work in Amsterdam.

This unattributed sculpture in Amsterdam is hiding in plain sight.

The attic of a four-century-old canal house hides a clandestine church.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

A formerly opulent Italian village is now a crumbling ghost town that no one really knows what to do with.

When Azorean green tea meets volcanic hot springs water, a luminous brew is born.

An Austrian house of bones filled with hundreds of intricately painted skulls.

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.

In Portugal, a secluded stretch of untouched natural beauty hides at the bottom of a steep hill.

Perhaps the most spectacular grotto along the Algarve coastline.

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

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.

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

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

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

Ring the bell to enter a bar that looks equal parts museum and old curiosity shop.

The world's oldest bookshop still in operation.