My time has come!
The above stereographic image is for cross-eyed viewing (most stereograms are wall-eyed, so you may need to put your finger in front of your screen until this one comes into focus)
This is an image of Honolulu, Hawaii, published by NASA. Note Diamond Head (the volcanic crater) in the south.
Here are some other stereopairs published by JPL:
Wheeler Ridge, California
Mount Saint Helens
Salt Lake Valley, Utah
Wellington, New Zealand
Yeah I found the poster's advice worked well. I.e. hold your finger between your eyes and the image and start focussing on your finger and them drop it away as the dots approach. It made me realize I wasn't normally crossing my eyes (for say, magic eye images), I was looking past the image and kind of uncrossing my eyes.
With these ones, they definitely work by crossing your eyes.