Within 1km of Seongsu Station are Daiso Seongsu 2-ga (106 Seongdeokjeong-gil) and Ttukseom Station Store (6 Achasan-ro), both open 10 am to 10 pm, so you can stop by after a pop-up. The ₩1,000 cylinder storage case is handy for carrying badges or a small plushie home.
