This reminds me that I've always wanted to make a huge interactive combinatorial circuit that computes SHA-256 and shows all its internal state, then put it on a site with the claim that anyone who can make its output match a certain clearly-constructed value (e.g. 0123456...ABCD...) will win a prize. No mentions of hash algorithms or other such phrasing to deter anyone. I wonder how many people would try such a "logic puzzle", how much time they'd spend on it, and if we might even get the first successful preimage attack from that.