@Slimer_J_Spud - anaglyphs are the cheapest way for 3D, they are easy to get a 3D effect but have the disadvantage of colour, and if viewed without goggles look mostly not very appealing.
Cross-viewed 3D images can be beheld even without any tricks, though without 3D effect. I’m not good at cross-eying and I agree that an object that is easy to fix is of great help. Once I get it, I can also move without losing it, but I get a hefty head-ache quite soon.
Parallel viewed 3D images come very easy to me. I just defocus until the pictures merge, then focus on the 3D result. No problem of losing it, Problem is, since they must not be wider than the eye distance, they are small. There are/were cheap viewers around for prints with an optic that helped looking parallel and magnified the picture a bit. I have over 50 renders I made for parallel 3D (2 renders with the camera a bit moved), put them side by side in a new picture and had prints made of them,
3D viewing has been around since photography started, 1880 or so. They were fashionable at some time, disappeared, reappeared, etc. I think composing 3D scenes in Bryce and then view them also in 3D is fascinating.