Hundreds of secret cabinets built into the walls of legendary poisoner's private work room.

The mystery of this small, brick pond eluded its possibly only investigator until his death.

This natural sea cave hides a small wonderland of natural turquoise beauty.

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

Statue of a decomposing prince that once held his heart in its hand.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

Europe's second largest ossuary wasn't discovered until 2001.

Museum deep in the catacombs of St. Michael the Archangel Church is explored by touch, sound, and smell.

After the famous composer died in Paris, his sister snuck his heart out of the country to honor his wish that it be buried in their native country.

Skulls from the plague of 1656 and World War II bombings are united by a cult dedicated to caring for the ancient dead.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

The silly symbol for an underground protest group is now scattered around the city.

Skeletons dressed in extravagant 18th century royal costumes cavort in the aisles of this German basilica.

A dead saint, a deadly poison, and a mysterious holy ooze.

A beautiful but toxic fountain of mercury.

The sign at the garden gate reads: "These Plants Can Kill."