Looking at google maps and airports for years every day.
I have some sort of photographic memory for that stuff, so yeah, there aren’t too many major airports out there that I don’t know yet. Admittedly, eastern Asia is an exception, though. It’s hard as there are countless large airports with names that are insanely tricky to remember over there.
Zhengzhou, Guangzhou, Shenzen, Qingdao, Chongqing, Changsa… it’s not possible for me yet to link such cities with the respective airport yet.
But yeah, I’m getting there.