Something you're just good at with minimal effort and/or you learned much more quickly than average.
For me, it's paper snowflakes. My brain just seems to effortlessly figure out what cuts to make to the paper wedge to make it turn out exactly how I want it. Largely useless, but good fun and was a much-needed ego boost when I was a kid :]
Mechanical adept here too. I am very good at holding and manipulating 3d objects in my brain, so I can kinda always just tell how something goes together to work.
I lived in Canada for 6 months surviving on nothing but being a medical Guinea pig (I had no working permit and due to anonymity, very little was asked of people participating in medical trials, plus they paid a decent amount especially if pain or discomfort was involved); as part of this I went through a raft of IQ tests (there was always some gambling addiction trial going at UofT for some reason) and found out that, like you, I have exceptional visual intelligence - rotating objects in my head, and figuring out if something would fit together was super skills of mine. In every other way I’m decidedly average.
Wow we're actually very different there. My visualization skills suck. Like, I've tried that thing where you imagine an apple in your head and rotate it, but I can't even fully visualize a 2d apple. If I'm looking at a system though, I can just understand how it works without visualizing anything about it. Because of that, I did have to draw out some diagrams from the word problems on the aformentioned military test...
Probably a major part to why I'm still not fully convinced I'm actually doing anything out of the ordinary. I'm not using any special skills or anything - the questions on that test felt to me about the same as asking "what would happen if you pushed this wheel from the top of this hill".