No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

The curious underground history of keeping Paris clean.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

Hidden behind a wall for decades, this masonic lodge was only rediscovered during renovations.

Museum dedicated to the terror regimes of Hungary.

2300-year-old Roman road connecting the empire.

This picturesque mansion has gone from opulent ruin to nature museum.

Indents in the pavement are all that remain from a grisly death machine in Paris.

The palace of the King of Kings, burned by Alexander the Great.

A museum dedicated to the Spanish occult in a town that was terrorized by the Inquisition.

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

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

The 1936 Summer Olympics site is a crumbling remnant of sportsmanship and a history its host country would like to forget.

This Irish show cave is said to have been the site of a Viking massacre that claimed 1,000 lives.

The oldest Italian café in Boston, this spot also serves as a veritable museum of vintage coffee ephemera.

The eccentric mansion of one of the most popular horror authors of modern times.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

Nonprofit art center that promotes outsider, intuitive, and self-taught art.

A legendary speakeasy bookstore returns from the brink.

Great place to have a drink and a bite to eat in an atmosphere laden with New York's Bohemian past.

One of the most popular megalithic sites in Ireland stands as a humbler version of Stonehenge.

This grand gothic brewery has been pumping out suds for over a hundred years.

Huge masonic hall in Philadelphia with lavishly themed rooms.

Sitting on an Italian hilltop is this surreal fortress built by the mad inventor of electrohomeopathy.