Challenge #64 is Jason Ku’s Bicycle v1.8. I feel like this is one of those more academic models, showing techniques for making wheels and bars that you might not think would be possible from a square of paper.
The bars that form a “V” lightly lock in to the lower horizontal bar, but they keep coming loose in mine. The most prominent feature is the wheels, but it has a seat, handlebars, pedals, and a kickstand.
I don’t really find a bicycle an “exciting” origami model, but it’s really fascinating that it can be made from a flat square without cutting it.