This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

Where commuters walk through remnants of an ancient Greek necropolis.

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

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

A historic Montreal market that was the city's agricultural hub for over century.

A grand Gothic Revival basilica with stained glass depictions of Montreal's religious history has only one soul resting in its crypt.

One of the indelible moments of the American Revolution took place at this location.

This area was once known for being a lawless haven for rough-and-tumble sailors, earning the maritime-themed nickname "the black sea."

The site of Paul Revere's historic two lantern warning.

This massive tea kettle was once a promotional stunt for the Oriental Teashop.

The American Revolution was galvanized into serious action due to the tragic clash with British soldiers that occurred at this location.

The former site of an all-but-forgotten colonial landmark is now remembered by an often overlooked bas relief.

The Boston square dedicated to the dark poet who was born nearby.

A men’s restroom became a sandwich shop.

Mrs. Mallard and her brood are a beloved fixture in Boston Public Garden.

Ice cream stand, snack bar, and time capsule of milk conveyance.

A plaque memorializes the Boston location of one of the largest nightclub fires in history.

The history of the tea trade is told in bas-relief on this historic pair of Boston doors.

American revolutionaries and British soldiers alike are buried here in the fourth-ever cemetery in Boston.

This bridge was the birthplace of a unit of measurement based on a fraternity joke.

On a former island, this old fortification once used to protect the Boston Area and started Edgar Allan Poe in his military career.

This Dutch-styled residential building was originally a cocoa company's World's Fair showpiece.

The 1920s child prodigy author was last seen here at her Brookline home before vanishing at age 25.

From bench to vandalism to art, this silly prank seat was funny enough to become permanent.