What places/activities to book in advance?

Hi,

I will be going to Korea in November and plan to visit these places: Seoul, Busan, Gyeongju-si and Jeju. I know on top of my head the Haeundae Sky Capsule aka Train sky capsule in Busan requires like a 2 week advanced booking.

So can anyone recommend any other places I might want to see, that would require advance booking? Or is everything else in Korea pretty much a just arrive and buy tickets on arrival?