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

The only structure left with direct ties to the Salem witchcraft trials of 1692.

France's national museum of scientific and industrial instruments.

A memorial to the nearly 10,000 American soldiers laid to rest on the beaches of Normandy during WWII.

This enormous "cloth of the conquest" depicts the Norman invasion of England in mind-blowing detail.

The first woman in America to receive a medical degree.

The world's oldest individual clonal tree looks like a wimp despite standing tall for 9,550 years.

Once thought to be the oldest living tree in the world, Methuselah was germinated before the Egyptian pyramids were built.

An abandoned Gold Coast-era mansion once intended for the exiled ruler of Albania, who never arrived.

A unique local art exhibit that has continued to grow since 1989.

Historic, 19th-century wagon wheel ruts cut into soft volcanic ash.

A breathtaking 19th-century trail overlooks Lake Tahoe.

The longest non-mortared wall in the country is one man's tribute to his displaced Yuchi ancestor's five-year journey to her homeland.

Walk a trail through a historic Quaker town that outlawed slavery in 1777 and was a major waypoint on the Underground Railroad.

The Beaux-Arts aquarium boasts a vast collection of saltwater and freshwater fish on an island in the Detroit River.

The taxidermied remains of Charles Dickens' pet raven, which helped inspire one of Edgar Allan Poe's most famous poems.

The "last unrestored grand mansion of Savannah" is now a cramped, mouldering maze of antiques.

The humble beginnings of one of America’s greatest songsmiths.

This bar hosts an ever-evolving napkin art installation devoted to an American president.

This kitschy tavern is also home to rare early editions of "Treasure Island."

At the turn of the 20th century, the Minnehaha County courthouse played host to sensational public divorce trials.

One devoted couple has donated multiple recreations of Michelangelo's sculptures to this South Dakota town.

This 22-acre botanical garden is home to the largest collection of rhododendrons in the world.

Duluth mineral magnates built this charming art deco lodge to be their private clubhouse.