This sinkhole in the Arizona desert is filled with carbonated, arsenic-rich water

This little brick tunnel built by Confederate forces was used to conduct surprise attacks on the railroad.

This historic Union Pacific Railroad depot is a stunning symbol of American post-Civil War progress.

America's post-nuclear-attack chambers of Congress.

The romance of early commercial flight still fills this Art Deco destination.

An easy-to-miss garden in Boston's North End honors the mother of JFK and others who lost children in WWII.

Dedicated to nine marines from Massachusetts who perished during the Beirut bombings.

The site of one of the strangest disasters in history—a wave of deadly molasses traveling at 35 mph.

Silverware in the sidewalk outside a grocery store cements this neighborhood’s Italian culinary history.

What was once a true peninsula has now been filled in, causing the water to recede and leaving many streetside "waterfronts" and landlocked "islands."

A mysterious stone embedded at the base of a historic Boston building.

This nearly 200-year-old restaurant's history includes an exiled French prince, JFK, and a very hungry Daniel Webster.

Millions of numbers carved in glass represent the tattoos forced upon victims.

"Mock all and sundry things, but leave the saints alone."

A centuries-old church stands as a testament to Boston's "father of architecture."

This ambitious father and son team reigned supreme over the North End, and witches, for many years.

The oldest Italian café in Boston, this spot also serves as a veritable museum of vintage coffee ephemera.

This research center for rare prosimians is studying how they sleep to help prolong human life.

A deep mark on the remains of a Roman temple, believed to be left by a legendary warrior.

Look closely and you’ll notice that the color changes a third of the way up the tower.

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

An overlooked memorial honoring the local Washington residents who died in World War I.

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."