Maybe not what you’re looking for because it’s not like one hard problem but more like many problems in a row, and generally I don’t really know whether they are difficult enough, but you could (have someone) look into Exit games. Those are basically like escape rooms to go. I’d filter for Age16+ to hopefully filter for the hard ones, though maybe you’d want to separately look up which are particularly hard.
I did one or two when I was like 15 or 16 years old, and recently remembered them and I want to try some more for fun (and maybe also introspection), though I didn’t get around to it yet. I think they are relatively ad-hoc puzzles though as with basically anything you can of course train to get good at Exit games in particular by practicing. (It’s possible that I totally overestimate the difficulty and they are actually more boring than I expect.)
(Btw, probably even less applicable to what you are looking for, but CondingEscape is also really fun. Especially the “Curse of the five warriors” is good.)
Maybe not what you’re looking for because it’s not like one hard problem but more like many problems in a row, and generally I don’t really know whether they are difficult enough, but you could (have someone) look into Exit games. Those are basically like escape rooms to go. I’d filter for Age16+ to hopefully filter for the hard ones, though maybe you’d want to separately look up which are particularly hard.
I did one or two when I was like 15 or 16 years old, and recently remembered them and I want to try some more for fun (and maybe also introspection), though I didn’t get around to it yet. I think they are relatively ad-hoc puzzles though as with basically anything you can of course train to get good at Exit games in particular by practicing. (It’s possible that I totally overestimate the difficulty and they are actually more boring than I expect.)
(Btw, probably even less applicable to what you are looking for, but CondingEscape is also really fun. Especially the “Curse of the five warriors” is good.)