Cheonggyecheon Stream.
Seoul is smartening up its act with this streamside passegiata that whips you right through the middle of town and rolling city vistas. Start at Cheonggye Plaza in Gwanghwamun /청계플라자 / and get off at Dongdaemun (see Shopping/Dongdaemun) / it takes around 2 hrs, and is perfect for late afternoon or early evening