Yesterday, I saw Betty Boop and the Little King. It was made in black and white in 1939, and I mention it because there’s a rather impressive 3D effect at around 1:50 (then again later).
Here’s a link from Archive.org if you prefer, but I had less luck with their embedder.
What I like about it is how it was achieved. It was done the same way all visual effects in the 30s were done: they built the thing and pointed a camera at it. That approach wouldn’t even occur to us now.
They had an entire rotating set built to create 30 seconds or so of footage.
I really like a lot of the CGI stuff we have now, and when it’s used well it’s just flawless, but it’s almost impossible to feel a sense of wonder at a visual effect in a modern film because it’s sort of clear how all of them were done. And there’s an elegance to the 1930s solution that the modern one lacks.