Built hundreds of years ago this downtown iron barrier once protected a much despised king.

This Wall Street bar was once a hub of revolutionary activity where Washington famously bid farewell to his troops.

Try not to get slimed in Tribeca.

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

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

Slyly buy a shake in the Parker Meridien lobby.

Once considered the height of medical modernity, this structure is now the oldest remaining component of Roosevelt Hospital.

Bowl in splendor, if you're lucky.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

One of the last few places in Manhattan that employed a pneumatic systemic keeps it on display.

A military vehicle collection, showcasing how war transportation advanced from horse drawn artillery to self propelled cannons.

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

A bunker "with enough U.S. currency to replenish the cash supply east of the Mississippi" in the event of nuclear war now protects nitrate film.

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

Experience a quartz crystal sound bath inside a storied, all-wood sound-chamber.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

A monumental statue of RCA's mascot now sits atop a historical society roof after a life of moving around.

A modern tower, symbolizing the legend of a golden egg on top of the tree of life.

An entertainment center in a huge transparent tent.

Iconic pyramid from famed British architect Norman Foster designed to represent all of the world's religious faiths.

105-foot wide giant metallic flower blooms anew every day in the heart of Buenos Aires.

Museum housed in underground tunnels that date back to Buenos Aires's earliest settlements.

A tower devoted to — and modeled after — the Divine Comedy.

This giant power line tower is a robot that can express its moods in neon.