This dilapidated castle-like structure overlooks the Hudson River at one of its widest points and was once home to nuns.

Abandoned concert venue legendary for its rock counterculture.

Ruined pieces of stone and a swimming pool are all that remain of an amusement park swept away by a flood.

Knoxville’s architectural icon was the symbol of the 1982 World’s Fair, even catching the googly eye of Bart Simpson.

A plaque marks the site directly below the mid-air detonation of the atomic bomb over Hiroshima.

The secret city built by the Manhattan Project.

Arguably the best example of an authentic Dutch windmill in the United States, rivaling its counterparts in the Netherlands.

A big museum full of little worlds.

One toy collector's legacy of hundreds of unique items includes the most diverse display of northern indigenous dolls.

A record-size collection of wild-haired troll dolls tells the story of the mythical creature's roots in Scandinavian folklore.

Ohio's 19th-century communist micro-society.

Mausoleums, astronomy, and animatronic dinosaurs at this memorial to an assassinated American president.

A former plague hospital turned medical museum.

This small museum displays a collection of outsider art and scale models of past "treatments" for mental illness.

The bears of Bern have been a city highlight for over 500 years.

This simple apartment may have inspired some of the most important theories in the history of science.

A nearly 500-year-old sculpture depicts a man eating a sack of babies, and no one is sure why.

More than a century of radio history is told in these displays.

A surprising museum of 20th-century technology.

Its vast collection of wondrous gadgets details the fascinating history of information technology.

The shelves in the back of this thrift store are devoted to saving, not selling, retro tech.

This Cold War missile launch site has been abandoned for 40 years.

Three abandoned missile silos are hiding in plain sight behind a suburban development in Maryland.

A Cold War secret surveillance tower used to spy on radio communications.