After heading back to Hongdae to find Karaoke, we actually ended up staying overnight at a multi-entertainment room. I'm not really sure what to call it, but we went out around midnight looking for a karaoke place and ended up at this business that had karaoke, movie facilities, wii and board games. We sang karaoke and watched movies - leaving around 5am. It cost 30,000 won for 12-8am, so it was a pretty good deal and experience. As we were walking home, we were amongst all these late night/early morning clubbers who were probably trying to catch the first train home.
The next day we headed across the river making a stop at Kyobo book store in Gangnam to purchase some albums from their Hot Tracks section, before heading to Coex. When we previously came to Korea, the Sum store was still being built and so we were excited to finally go in.