A semi-scholarly approach to sex.

The ruins of an 18th-century mansion that was once named "Mistake" by the man who had it built.

The hidden ruins of a mill that is linked to an attempt to assassinate the vice president of the United States.

A historic ruin just 20 feet away from a busy highway onramp.

A derelict bit of transportation infrastructure hidden in the woods.

One of only two commuter aerial tramways in the United States.

A former poultry store that looks like a giant duck and is one of the "seven wonders" of Long Island.

This 19th-century Hamptons windmill was once home to modernist painter Agnes Pelton.

Built in 1815, the stabilized ruins of the grist mill and sawmill are now gated, but interpretive displays on the features and functions of the mill preserve its history.

This beloved Baltimore spot features caged dolls, a giant Pez collection, and many, many mannequins.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

This free, take-a-book shop seems like a trick but isn't.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

Elevated freight railway turned wildly successful urban park.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

World's first "penitentiary," meant to be humane, drove men insane.

This ruined quarry once produced the distinctive red sandstone used for construction projects in Washington, D.C.

A labor of love built by local hang-gliding enthusiasts, this ideal launch spot was outlawed by the authorities and has since been largely abandoned.

A mammoth pair of Civil War artillery guns abandoned out in the forest.

This palatial botanical garden is home to one of the largest pipe organs ever installed in a private residence, and a piece of Wood's cycad.

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

The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

The land is home to swimming ponies and a legendary 18th-century treasure.