I missed it—did you? Wednesday, March 22, was National 3D Day (celebrated on the 3rd day of the 3rd full week of the 3rd month—get it?)
But it's not too late to celebrate and enjoy some history of 3D by making a virtual visit to 3-D SPACE, The Center for Stereoscopic Photography, Art, Cinema and Education Museum in Los Angeles.
You can see the current installation "Not Just a Kid's Toy," a terrific collection of ViewMaster viewers, projectors, cameras, and more. (I've got my own Personal VM camera, VM Stereomatic 500 projector, and several VM viewers–cool to see those in the collection!).
If you can visit in person, look on their calendar of events for 3D movie screenings, like The Black Lagoon from 1954.