In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

An artsy hidden staircase leads to breathtaking views of San Francisco.

Apartment complexes built into huge repurposed natural gas tanks.

A layered tribute to the work of mosaicist Isaiah Zagar.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

The yawning maw of this pagan visage is said to bite off the hands of liars.

2300-year-old Roman road connecting the empire.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

Go inside to really appreciate this 500-year-old technological masterpiece.

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

Pompeii's less famous neighbor is still revealing her secrets.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Budapest's Communist-era statues, banished to the suburbs.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

An intricately designed junk art house with four extravagant junk art cars hidden in the suburbs.

Remnants of a storybook amusement park hidden behind a strip mall.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

The site of the climactic scene from the classic horror film is now a historic landmark.

A local farm's collection of unusual structures from a now defunct storybook amusement park.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.