'The Letters of Utrecht' lays out a ribbon of poetry one letter at a time, with no final verse in sight.

The world's largest bicycle shelter can hold more than 12,500 two-wheelers.

The location of the world's first telescope demonstration.

This unattributed sculpture in Amsterdam is hiding in plain sight.

This massive mural by famed pop-artist Keith Haring was hidden for almost 30 years until its 2018 rediscovery.

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

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

A beautiful geyser under environmental threat.

Crypt mausoleum in cathedral's basement contains relics of third century Roman martyr, Saint Vibiana.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

Famously misunderstood wonder of the ancient world

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

The first declared National Monument in the United States.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

A beautiful Victorian-era cemetery, complete with a miniature village.

Banksy gives themself artistic license with this piece of London street art.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

America's most famous piece of self-built architecture.

This massive library holds what was once the largest book collection in the world.

The oldest family-run luncheonette in New York, last renovated in 1948, still serves food and drinks the old-fashioned way.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

The only structure left with direct ties to the Salem witchcraft trials of 1692.

The legendary building that needed ghostly approval before being built.

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