A hidden bathhouse in one of Stockholm's oldest and busiest neighborhoods is open to anyone who can find it.

A historic arena where the Beatles played their first concert in the U.S.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

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

Largest Roman Catholic church in North America.

A haunting tribute to pioneering photographer Clover Adams.

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

The privately owned cemetery that holds room for Washington's finest when they step down from life.

A super-sized promotional trick that is now a D.C. landmark.

The origin of this mechanical boy was a mystery until he revealed his maker by writing it in perfect cursive.

This little-known collection holds everything from "Dracula" notes, to the manuscript of "Ulysses," to the forged works of Shakespeare.

The world’s first penitentiary, meant to be humane, drove men insane.

Golden and naked, the figure that was once the highest point in New York is all that remains of the second Madison Square Garden.

Yo, Adrian!

Dr Barnes' $25 billion private collection of art and arboretum.

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

One of the oldest log cabins in America is one of the last of its kind this historic Swedish dwelling remains a piece of living history.

One artist's love letter to his city and its citizens plays out across dozens of bright murals painted on the sides of decrepit buildings.

A layered tribute to the work of mosaicist Isaiah Zagar.

An Irish Memorial commemorating those who perished due to potato blight.

The body of St. John Neumann and his collection of hundreds of relics, on display in a Philly church.

Tour the dark and beloved poet's former cobwebbed basement, which may have inspired "The Black Cat."

Instruments, apparatus, and rare books all relating to chemistry and its related sciences.

Mural made of 100,000 pieces of hand blown glass, and one of the largest glass murals in the US.