An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

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

This fertility idol of questionable authenticity inspired an iconic Indiana Jones artifact.

Once America's tallest structure, now a Baltimore landmark.

This bug-eyed water wheel uses the power of the Sun to clean up Baltimore Harbor.

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

A massive, majestic mammal watches over pedestrians from his perch atop a former B.P.O.E. lodge.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

An original apothecary from 1792.

A former major munitions plant that has been converted into a sprawling art space.

A superbly preserved example of Georgian residential architecture that was once home to one of the founders of Alexandria, Virginia.

This small pedestal marks the spot of the first lot of land sold in Alexandria, Virginia in 1749.

The narrowest house in America is seven feet of pure spite.

This colonial tavern played host to George Washington, Thomas Jefferson, and other famous early Americans.

This advertisement for talcum powder was painted on the rock face and has since defied removal.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

The only surviving 19th-century water-powered mill found in the Washington, D.C. area.

This unique art installation used boiler tubes from a decommissioned power plant to resemble Antelope Canyon.

Overlooking the Colorado Convention Center is this giant sculpture made from thousands of triangles.

A downtown park built on top of unclaimed graves.

Iron Age runes and ruins hide in plain sight along this Portuguese beach.

The world's oldest bookshop still in operation.

A gaudy painted elephant stands in memory of south Florida's fallen carnies.