An Industrial Revolution-era public work that purified water using nothing but sand.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

A historic neighborhood church is reborn as a psychedelic arts collective.

The site of the climactic scene from the classic horror film is now a historic landmark.

The United States Capitol's former columns still stand.

Just outside of Jordan's capital lies an ancient castle and intriguing caves dating back to the Copper Age.

The most gigantic, swoony, intimidating trio of fingers in all of antiquity.

Standing atop 2nd-century Roman ruins, this church is one of the oldest and most iconic in Old Cairo.

An ancient instrument used to measure the waters of the Nile so Egyptian farmers would know whether to expect famine or flood.

The massive cave church of Cairo's Zabbaleen community is one of the largest Christian churches in the Middle East.