Oooh what's it like in teaching in China? I'm considering teaching EFL again next year but not sure if I could hack China.
English wise, you should be fine if you've managed in China. From what I remember signs are bilingual in Seoul and Busan. I found that English wasn't really spoken, especially by the older Koreans. The ones that travel tend to be much more confident with it!
In Seoul, my favourite area is Hongdae, if I was going to go back to Korea I'd like to live there or Busan. It's just really cool, and the best night out! Check out one of the palaces, I liked Gyeongbukgung. And one of the Hanbok villages (I liked Namsangol).
Insadong is worth going to, it's the traditional area, lots of tea rooms and a great place to pick up gifts. I'm not sure if it's true or not, but they say it's the only place where even the big brands have to have their logo written in Hangul. It's quite cool seeing Starbucks and McDonalds in Hangul rather than English.
N Seoul tower is awesome, and in the evening they project light shows onto the tower. I'd also recommend Seoadaemun prison and the war memorial.
I don't know if you'll be able to given the current situation but if you get the chance, a trip to the DMZ is well worth it. I went with the USO and the tour is given by the US soldiers. (
http://affiliates.uso.org/Korea/?contentid=347)
I always went around Korea by bus rather than train, they're almost as quick, super cheap, and ridiculously luxurious. The buses only have 3 seats an aisle and you can recline really far back, and the foot rest comes right up. And there's so much room between each row that the person behind you will barely notice, even if you recline almost horizontally. Not the best picture but you get the idea! You always stop at a service station halfway through the journey, and they're an experience in themselves. Definitely get some hoddeok!
It'll be really hot whilst you're their too so try some Patbingsu, it's this shaved ice, creamy, fruity, cornflakey, red bean mixture.
I stayed in the Haeundae when I was there and I liked it, really close to the beach and plenty of places to eat/drink. I thought Haeundae beach was nice, and it wasn't too busy when we went. I've only been to Busan when there's been a festival on though, we went to the Sand Art Festival. This should give you an idea of the beach...
If it's too busy for you though, there's always Gwangalli beach.
Jagalchi fish market is worth seeing, you're bound to see a runaway octopus!
I didn't go myself but people recommended Haedong Yonggungsa Temple.
Phew, sorry that was longer than I expected! I've been home for a year and think I went on a bit of a trip down memory lane haha x