This is a very good example of a Keystone Stereoscope or Stereo Viewer. since does not have a patent notice, it was likely produced sometime in the early 1920s. It's amazing to think how old 3d technology is!
Operates perfectly. Gives a good, clear image. The card holder, handle, lenses, and velvet liner all are in good condition and appear original. The finish on the bent wood hood does have some scratches. These could be repaired with a bit of paint, or even just a brown marker, but we like to leave things "as found".
There's a stero view card included. It shows "Tiber and Saint Peters Church, Rome Italy". It's a lithographic print type. According to the notices given in the red scrollwork, it was taken from original stereo view photographs, by the HC White company in 1905.
Very cool piece of old tech entertainment. We have lots of other cards available too.