An eerie cluster of medieval cave-like tombs carved out of a cliff, hidden in a historic mountain pass.

Austria's very first and only nuclear power station was completed but never used.

A full-scale sculpture of a mermaid and baby grand piano hidden underwater by David Copperfield.

This lower Manhattan bar is set up in an old bank vault that rests beneath a skyscraper that hides even more historic splendor.

One of the last functioning antique elevators in Chicago.

Less a museum than a bizarre fantasy world created by artists and engineers.

This shop for all your super spy needs hides an educational secret.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

Enormous lake at the bottom of a unique cave system.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

The United States Capitol's former columns still stand.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

Twice a year, visitors can tour the desolate site that birthed the Atomic Age.

This memorial plaque remembers a strangely shallow maritime disaster known as "Chicago's Titanic."

You can take a class, browse the library, or visit the lavish lair of an international men's humor society.

One-of-a-kind preserved ruins of an abandoned 1880s church in Chicago's Pilsen neighborhood.

Chicago's largest cemetery is full of beautiful Victorian monuments and more than a few ghost stories.

A gothic church spire sits atop this skyscraper, the tallest church in the world.

Chicago's North Park Village was once the largest municipal sanatorium in the country.

A lush green oasis in the middle of Chicago.

A century-old hotspot for jazz, frequented by everyone from Charlie Chaplin to Al Capone.

This morbid, delightful curiosity shop offers everything from animal bones to human teeth.

The subtle science of a master molecular gastronomist.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.