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 :]
If you’re ever bored one night, close your eyes and get a friend to rotate you around (gently and slowly) then get you to turn yourself to point where you feel north is. Do this 10 times, logging how far of you were from north and see how accurate you are from random.
You might have a hidden sense that’s incredibly rare in humans!