Very clean, efficient & extensive network Metro. Stations are huge, with extensive walking & stairs climbing for transfers. Seoul Station itself is super huge - like a mini underground city. Some stations do not have escalators , so you need to lug your heavy luggages up & down many stairs. Limited lifts are available, but very small ( & meant for elderly, pregnant women, wheelchair bound, etc). Of course one can use it if carrying heavy luggages. We have visited Korea many times & in our opinion, we always felt that the stations are not user friendly for travellers esp with luggages. Long queues & long wait to take limited small lifts, which you have to share with the mentioned locals group. Also there are no station counters if you need help or make enquiries. Many years ago, every station has a counter, but no more. Keep enough small notes for topping up cards.