In Myeongdong, go to Daiso Myeongdong flagship (43 Myeongdong-gil) or Seoul City Hall Plaza (93 Sejong-daero), both 10am–10pm. The Extra Super 9 Plus line has an acne cleansing foam (100ml) for ₩3,000 with 30K orders. At 100ml it fits your 1L carry-on bag, and City Hall store is handy after Deoksugung. Get all three in one stop.
Daiso Mall
Daiso MallDaiso Mall