One of my favorites is Bellman's Lost in the Forest Problem. It is a 2D geometric problem that is easy to state, understand, visualize and draw. The escape path is unconstrained, so there must often be a series of rules and decisions to be made. Some doodling quickly reveals its subtlety.
It is also nicely phrased as a class of problems, because the forest's size and shape are known to the victim, but there are no constraints on what the shape might be. Some of the classes are solved, so you can chase down the spoiler solutions, but others are still open.
It is also nicely phrased as a class of problems, because the forest's size and shape are known to the victim, but there are no constraints on what the shape might be. Some of the classes are solved, so you can chase down the spoiler solutions, but others are still open.
https://en.wikipedia.org/wiki/Bellman%27s_lost_in_a_forest_p...
Warning: don't read these unless you want your next weekend to disappear:
http://wardsattic.com/joomla/Download/BellmanForestProblem.p...
https://www.maa.org/sites/default/files/pdf/upload_library/2...
P.S. Previously on HN:
https://news.ycombinator.com/item?id=18001449
P.P.S. I have now added PDF links to the Wikipedia article.