This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

Hidden in plain sight on a pair of Manhattan subway tunnels are a pair of public instruments that sing to each other.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

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

Try not to get slimed in Tribeca.

The world’s oldest and biggest bookstore stocking only mystery, crime fiction, espionage, and thrillers.

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

The wooden grave marker of a railroad worker who died in a freak whirlwind.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

It's believed this well was once plagued with evil spirits until St. Columba purified the water.

In 1990, this 37-foot red steel bottle sailed from New York to England.

Now famous as the "Harry Potter bridge," this impressive concrete viaduct has long been an icon in its own right.

This life-size monument honors the legacy of a famous literary feline.

Before becoming a poet John Keats studied here to become a surgeon.

The world's largest collection of ship figureheads includes figures from legends and history alike, from Sir Lancelot to Abraham Lincoln.

Colorful murals by Jean Cocteau hide within this peaceful London sanctuary.

The commemorative stone column conceals a secret laboratory.

An architectural oddity hides in plain sight on this iconic London bridge.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Where condemned pirates met their grisly end at the gallows on the River Thames.

Dictionary Johnson’s favorite feline.

The London pub overlooks where the Mayflower was moored before setting sail for the New World.

Hear the quietest sound from across the dome.