Please DO Touch. Museums encourage visitors to handle and look through antique stereoscopes, to see photos rendered in 3-D.
In the age before radio and television, the stereoscope was very popular. Families had one in the parlor, along with many black-and-white photos, two identical photos on a single card. They bought the cards with the double images on them.
If you see one in a museum, pick it up and pull the photos toward or away from you until the image pops — they may be black and white photos, but the 3-D effect is vivid. Many of the photos are landscapes with depth, like the photos here. The one directly above shows a river in a canyon.
Most folks could not travel far, but a collection of these images from many places would be fun, and your friends would have a different collection in their home.