@c9a @futurebird Very cool!

I wonder how the puzzle was constructed in the first place. How did they find a configuration such that (a) they knew the shortest path AND (b) that path was very long and hard to find? I can see how to write a computer program to do it, but I assume that's not what they did. Maybe, as was mentioned elsewhere, there's an intuition one develops if one spends enough time on this kind of puzzle.