Mark Setteducati's book (with Anne Benkovitz), The Magic Show includes at least one example of two of the illusions presented on the website (equal color values appear different when placed in different context...)
I believe JonR posted about this elsewhere, but if you want to see more of this ilk (including more Jerry Andrus material and "dragon-like" perspective material), check out Al Seckel's The Great Book of Optical Illusions...
A mountain fold looks like a peak (^) while a valley fold looks like a valley (V). This is standard origami terminology. You can find a wealth of origami basics with a simple web search using your favorite search engine.
Try this Paper Dragon - you won't be sorry!
Thanks to Jerry Andrus, who inspired the creation of this illusion (which was presented during a gathering of Martin Gardner fanatics)
merlou, believe what the directions are telling you about mountain and valley folds. They are counter-intuitive and you will seem to be building the dragon's head inside out. But that is correct, and the results are amazing.