The personal charnel house of Anton Bruckner.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

This skeleton-filled altar piece served as a backdrop to one of the most iconic scenes in "The Sound of Music."

This 16th-century monastery has been turned into a surrealist architecture compound.

This abandoned island off the Venetian coast has been a radical monastery, a political prison, and a secret Nazi base.

Venice's island of the dead.

These gutted monastery ruins still stand proudly in the middle of the Italian countryside.

The forbidden island of the Tuscan Archipelago may still contain buried treasure.

An unsettling painting of three faceless sisters that is surrounded by history and legend.

This ancient ruined monastery has been destroyed by fire so many times that it seems like God hates it.

An ancient monastery, a locked room, and a mysterious book heist.

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

This abandoned Belgian fortress is purposefully being left to nature.

A magical and peaceful ruined Cistercian abbey in what is now southern Belgium.

The mental institution where Van Gogh created some of his most famous work now allows guests to walk in the artist's footsteps.

The world's toughest modern Christian pilgrimage leads directly to the gates of Hell.

A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

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

At the foot of a waterfall lies a peaceful swimming lagoon and evidence of over 60,000 years of human habitation.

An enchanting monastery in the Spanish countryside appears lifted from a fantasy tale.

A Romanian church built from one single oak.

Underground monastery and fortress.

This historic black and white monastery is one of Bulgaria's architectural jewels.

Nestled in a peaceful valley, this Armenian monastery may have been saved from Mongols thanks to the eyes of God.