in seoul go to itaewon station and look for the irish pub. there is a pool table, you can drink beer and the people there are friendly (like everywher ein korea...)
i enjoyed this pub because i don't like clubbing... well at itaewon there is a lot of clubs. btw, the last subway is at approx 1 o clock, so make sure you club near to your hotel
go to a jimjilbang (sorry got no korean keyboard, can't type it in korean), it's an interesting experience. it's also possible to sleep there (very cheap). if you are able to sleep on the floor, in a (imo very) hot room
yongsan station in seoul has a lot of electronics... interesting if you like electronics. not as cheap as in china, but still interesting to see the complex of thousands of stores...
order bibim-bap in a traditional restaurant (means mixed rice), somewhere where the tables are nearly at floor level
drink the 2 different kinds of rice wine, i think one is called "maccoli" and the i don't remember. especially maccoli is nice!