I used to love viewmasters! But they're pretty much history now.
You can make your own 3-D photos. Just focus on the subject, take the shot, move over a few inches and take a second shot.
Next, you need a viewer. There are many available. These hold 35mm slides.
These are made for viewing stereo aerial photos, but work great for my purposes.
I tape the prints to a piece of paper board to keep them in proper postion. Only one pair will fit in portrait orientation, but two pair will fit in landscape orientation.
This type of viewer is not very good as their field of view is small
Stereo pairs can be found online and printed. A lot depends on the quality of the printer though.
Adding the 3rd dimension (depth) to your photos makes them much more enjoyable.
Try it. I hope you like it!