This quarter-mile tunnel under the Bluff in Pittsburgh bends at a 45-degree angle.

An imposing pair of sphinxes stand guard outside this Egyptian Revival tomb.

This spot memorializes one of the greatest plays in NFL history, unless you happen to be a Raiders fan.

This public park was the site of the largest civilian disaster of the Civil War.

Once used to screen films for theater owners to rent, this historic building is now a start up hub.

Once the supplier for noteworthy projects like the National Cathedral, this old brickworks now lies abandoned.

This bridge over D.C.'s Rock Creek Park is sometimes called the "Buffalo Bridge" because of its four buffalo sculptures, which were cast from a single piece of bronze.

Railroad officials in the early 1900s sought to spare travelers the sight of Roman soldiers’ private parts.

This unassuming passageway played a key role in one of the most important events in U.S. history.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

The iconic D.C. restaurant where the Cuban Missile Crisis was negotiated, now a Walgreens.

The National Park Service’s best-kept secret with views that rival any in D.C.

This statue of one of baseball’s greatest pitchers looks like something out of a sci-fi horror movie.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

This forgotten boat elevator was an engineering marvel in its heyday.

Art deco landmark on the outskirts of Washington, D.C.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

A gorgeous mural outside a beloved D.C. restaurant pays homage to famous Black Americans.

Washington's iconic carousel has a nice piece of Civil Rights history.

The span is crooked and made from two older recycled bridges.

A clone of a cloned tree that was so important it allegedly had its own guards.

Sit where JFK proposed to Jackie or where Nixon dined on meatloaf at this storied pub.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

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