Shanghai's famous 100-year-old dumpling restaurant has two branches in Korea. One of them is (where else) in the Seoul Finance Center (the other is in Myeongdong). Although you can get dumplings much cheaper in other parts of the city, you'll never be able to beat the juiciness of the pork buns, or enjoy them in as sophisticated surroundings as these. There are other items on the menu, but the dumplings are what made this place famous. Try one of their signature pork dumplings, or such Korean-inspired specialties as chicken and ginseng, or pork and pine mushroom.
