I only post about video games here if it has value beyond the video gaming itself.
StarCraft 2, when played "competitively" (even just on the ranked ladder online, not necessarily professionally) is the single most intense mental exercise I know of.
Things like Rubik's cubes or chess or go, or advanced math problems, or holding in your head everything needed to design or understand a complex software architecture or design or algorithm, or a martial arts spar, or playing a musical instrument at peak ability, or simulating experiences and cognition, etc - all that pushes various different thinking limits too.
But StarCraft 2 1v1 ladder play, when you actually go at it as fast and effortfully as you can... Holy shit. It's anywhere from five to sixty minutes (depending on how well you and your opponent play) of non-stop brain firing on all cylinders.
There is always something more you could be doing, always more things you could be checking or keeping track of.
The game will consume and reward any improvement in multi-tasking or information processing or strategic judgment or world-modeling (of the game state) or mind interferometry (of the other player) or just raw speed and precision of movement that you can feed it.
Near as I can tell there is no ceiling. You can keep getting better forever, and you will still be able to get better at doing it, even if you do end up better than everyone else. Of course that is not unique - lots of games, and most deep real-life skills, have no ceiling.
It's the combination of simultaneous and urgent demands, the complexity and variety, and the lack of obvious ceiling, all together, that I find unique.
Now maybe there are other games like it and maybe other people get the same level of intense deep and broad mental challenge in other things.
For example, I predict that once developed far enough, and if approached with the same deliberate focused activated intensity, "humaning" can open up that rich unceasing explosion of challenge.
So there are probably other ways to get mentally exercised as intensely or more, perhaps even in the skills I mentioned earlier as not doing that for me. StarCraft 2 1v1 ranked ladder play just happens to be the most intense one I have had.
I do think I am onto something with the whole "if approached with deliberate focused activated intensity" comment though. I think part of why SC2 is so mentally intense for me is that I go into it feeling like it has to be.
But in the other hand, I think I am only able to feel that way because with SC2 I can see beyond my ability - I cannot do as well as I know can be done. Also SC2 only became this way for me when I saw by example just how fast it could be played.
Looking back, I have had moments of similar intensity when humaning. But only when things seemed like urgent theats or problems. But usually those were done as soon as impression management damage control was done, and only the most immediately relevant cognition flows of at most a mind or two had to be mentally handled.
Oh and when I got attacked by that dog five years or so ago - but again I won that too quickly, so the state lasted for literally at most five seconds. And there was so, so much less to that problem space. One human and one dog bodies' worth of anatomy simplified down to just the movement mechanics and vulnerabilities, the dog's mind, the one human observer in the room who literally did not even get around to moving in the time before it was over, background proceeding of peripheral perceptions for signs of people in the nearby rooms doing anything relevant.
That sounds like a lot, and maybe it is, but it is mostly interlinked in these smooth cognition flows that handle it all, while SC2 involves so much more that has to be individually and discretely mentally accounted for.
StarCraft 2 feels like it demands more of my mind than any of those situations, but most importantly - and this is the huge thing - it demands it for much longer periods of time, unrelentingly.
The hilarious thing is that a huge number of people play way better than me. I'm actually pretty damn sucky. So I suspect there is some way to just play it with way less mental effort and intensity and focus.
I have always been prone to exponential skill growth curves. I kinda suck at things, usually for years, until eventually I grind and stumble my way into finally getting a feel for the problem space and the skills and the cognition needed, and at some point it tips over and I start improving really rapidly. Then a few years later people assume I'm natural or talented or have always had a knack for it.
But anyway, I'm either still in what I suspect is the sublinear part of my SC2 skill growth curve, or just getting out of it. We'll see.
So there are probably ways to play, at least at my weak level, that do not provide that exercise, and we could probably find something else that does.
And also, I am not sure how much of the cognition I train up playing SC2 is actually transferable to other, more practical matters.
Anyway, I thought it was worth sharing that in the decade since it came out, I have basically found nothing else that exercises the mind the same way.