The oldest operating apothecary in the US has treated everyone from Thomas Edison to Mark Twain.

Cryptic messages embedded in the New York City sidewalk.

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

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

Plot your trip through the city on the sidewalk.

A hidden "place of interment for gentlemen."

Once the tallest building in the world and the site of "the highest dinner ever held in New York" this building now holds the most expensive penthouse in the city.

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

One of only two commuter aerial tramways in the United States.

A celebration of capitalism in Midtown.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

Read a book next to a Midtown waterfall.

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

Elevated freight railway turned wildly successful urban park.

Try not to get slimed in Tribeca.

An interesting decoration on this historic site, this weathervane comes with as many legends as it does questions.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

The site where Charles Dickens gave his first public reading of "A Christmas Carol" in the US.

Narrowest house in Boston.

Macabre headstones carved with winged skulls, dancing skeletons, and pithy reminders of impending death.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

This bronze boar's snout has been rubbed to a golden sheen by visitors seeking good fortune.