Took at 6 days / 5 night trip to Seoul a few months ago and it was great. It's my second time and I'm spending twice as many days as the last time. The first day was of one of rest, but I headed off early the next morning to the DMZ. The guided tour had several stops inside the South Korean side of the DMZ, with the key attraction being the underground tunnel that the North Koreans built to invade the south. Unfortunately, photography was not allowed at the tunnel and viewpoints overlooking the DMZ to the north was met with clouds and haze, so visibility was limited. The 3 stops in the DMZ allowed for souvenir shopping each time, but at a rather quick 15 minute period unless you skip the sights. Have I had known that each store sold similar items, I would've been less stressed out. The last stop was at a grocery store at a village and was probably the best place to pick up snacks and drinks as souvenirs as it had the most variety. Note that some food items could also be bought out in Seoul, so you're really just getting the DMZ version. There were some items, such as grape wine that comes from the North, but there are usually southern versions as well.The rest of my trip was filled with more standard stuff, such as the Hangang River cruise, a non-verbal comedy show called Bibap, a visit to a two temples, castle ruins with a great nighttime view of the city, and Gyeongbokgung Palace. I highly recommend the Bibap show because it was hilarious, especially if your friend gets picked to go on stage to participate, and the palace tour because it was just a beautiful location. While the tour guide told me a lot about the palace, I never got the chance to just roam about and enjoy the scenery. Oh, if you want to go to museums, do it any day except for Monday. Most of them are closed on Mondays!
Bigger than expected with many indoor exhibits, if you show up early enough. Wasn't able to find a good high point nearby to take an encompassing photo. There's a mall nearby that supposedly has a good view, but I showed up too late.