My parents visited me over summer vacation. The first night they arrived, I dragged them around Hongdae, as I had to pick up my passport. The second night, as per my dad's request, we hopped on the KTX. Since I had to work that day, we didn't have much time so we took a 1 hour trip to Daejeon, spent a few hours wandering around there and eating dinner, then hopped the train back to Seoul. A lot of traveling to do just for dinner, but the KTX is kinda cool.