Legend says this sacred tree was a gift from goddess Athena.

An ancient octagonal weather station named for the eight Greek gods of wind.

A 2,000-year-old computer demonstrates remarkable engineering and astronomical precision.

This fairytale-looking castle is a wonderful example of Greek neo-Gothic architecture

What once sat in the world’s spotlight is today a largely disused ghost complex.

This pink watchtower served as the seat of the Greek government after independence from the Turks.

This abandoned caretaker's apartment is one of 13 left in the New York Public Library system.

A discreet little stairway on St. Nicholas Avenue leads to a quaint and unexpected cobblestone street of 19th century wooden rowhouses.

The front yard of an Upper East Side town house hides the last fragment of one of New York's most famous theatres.

New York's oldest and possibly grandest keeper of books.

Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

The fanciest public restroom in New York City boasts fresh flowers, art, and a classical music soundtrack.

The famous facade of Grand Central Terminal hides a regulation tennis court, and it's not the first one.

Hidden behind a gate in Greenwich Village is a little farmhouse that once served as the writing studio of a bestselling author.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

A mysteriously dark cemetery monument fuels stories and legends galore.

A haunting tribute to pioneering photographer Clover Adams.

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

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

Also known as the Founding Church of Scientology.

Obscure Freemasons still live in D.C.’s largest private residence.

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

Remains of a historic fountain that was mysteriously lost in the demolition of a D.C. traffic circle.

A master of deception, Harry Houdini's greatest trick may have been living in two places at once.