If you are thinking on visiting some other places rather than Seoul, Gyeongju (경주시) might be a good choice. The city offers many historical sites from the Silla Dynasty such as Seokguram Grotto, Bulguksa temple, the Royal Tomb Complex, the Cheomseongdae, which is one of the oldest astronomical observatories in East Asia and the Anapji royal pond garden. I have been to all of these sites before and they are all interesting, but if you have limited time, I recommend visiting these three: Anapji, Seokguram and Bulguksa. I wish I had photos of all of these attractions, but the first time I was there I had a really old camera and the photos are not presentable. This time we picked the day with the worst weather and it was raining cat’s and dog’s by the time we were finished with Seokguram and on our way to the Tombs. All sights are in the open and it was not worth getting soaked in the rain.
The other side of the river
COEX, Lotte World Tower, Gangnam
I wish we would have done something different instead of going to COEX, but I wanted to visit an aquarium with my mom. To be honest, COEX is not the best choice, although they do have some impressive sea life in there, but I think a lot of the fish tanks are too small. I honestly felt bad for all the animals at some point. COEX itself contains convention centers and exhibition halls as well as a shopping mall with a lot of restaurants. It is easy to find, there are two subway stations which come in question: