Back in about 1960, Weetabix put 3D stereoscopic cards in its packets. My dad's dad collected them, and about 10 years later gave them to me and my brother. You needed a device called a Vistascreen to see them:
That one is in cream, but the one we had was in red. My brother wound up with ours, so I bought this for myself off eBay. It doesn't have as many cards as we had (my grandad was very good at collecting things, as the 26,000 matchbox labels in our attic testifies), but it does have some I remember. The one shown in the Vistascreen there is Girl with Leopard, which is so good when you look at it through the viewer that you can really see the double chin on the "girl".
Here's what the card looks like up close:
You have to use the diverge-eye technique to see the 3D without glasses, as the images are the wrong way round for the much easier cross-eye technique. I've made an animated .gif of it, but it doesn't work at all well:
See?
The backs of the cards have descriptions of what's on the front. Some of these read as if the person writing them has been doing it all week and it's late afternoon on Friday. The one for Girl With Leopard is particularly charming for its 50-years-ago aesthetic:
I'm going to have to go back to eBay now to buy some more cards. There's a particular one of someone working on a girder high up in the sky that I want, and another one of fish in a pool that's pretty good.
To the Internet!