A 98-room castle in the middle of Toronto that bankrupted a 19th century electricity multimillionaire.

19th-century operating theatre in which the use of ether was first demonstrated - plus, a skeleton and a mummy!

A plaque memorializes the Boston location of one of the largest nightclub fires in history.

This Dutch-styled residential building was originally a cocoa company's World's Fair showpiece.

This Boston medical museum features the skull of the famous medical case of Phineas Gage.

Museum dedicated to awful artwork.

Rising 30 feet in the air atop Quarry Hill, the Old Powder House is the oldest stone building in the state of Massachusetts.

This tiny, painted door at the base of a tree stump has been a fixture of the Harvard University campus for decades.

A tiny collection of traditional Japanese woodblock prints, open only when the owner feels like it.

The self-proclaimed world's smallest museum, located next to a Massachusetts sandwich chain.

The Boston square dedicated to the dark poet who was born nearby.

Visible below the waves are memorials to the city's Gold Rush dead.

A nondescript building that's been functioning as a speakeasy for nearly a century and a half.

A museum befitting the city responsible for supplying the majority of the world's LSD.

A 140-year-old castle with underground caves hidden in San Francisco.

A huge musical instrument played by the ocean.

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

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

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

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

An small and easily overlooked archaeology museum chock full of Egyptian artifacts.

A naturally mummified 2,000-year-old man.