Visit the Smithsonian's stereoviews
The Smithsonian's Photographic History Collection contains more than 35,000 stereoviews.
The photographic technique of stereoscopy has been around since 1838. This technique uses two photographs taken from slightly different angles, viewed together using a stereoscope. With the 150th anniversary of the start of the American Civil War, the Smithsonian Institute has unveiled a collection of stereograms from the battlefields, camps, and cities affected by the war.
The Smithsonian's Photographic History Collection contains more than 35,000 stereoviews, many of which can be seen in their online collection. More animated examples can be seen in NPR's article.