COEX Intercontinental Hotel - in an area like 国贸. One of my favorite hotels in Seoul. You should be able to find some bars in the area. If you want to have a bit more fun, suggest you go to Itanwon (梨太院), check out the bars on the side streets.
Grand Hyatt - Another one of my favorite hotels in Seoul. On the other side of the Han river. Nothing nearby though. There is a night club in the hotel. If you know Grand Hyatt, you know what kind of the nightclub it is.
