Nine Hertz 9HERTZ is a two-floor cafe near Wangsimni Station in Haengdang-dong, Seongdong-gu, Seoul, selling coffee and desserts. Its menu includes scones, cookies, vanilla frappe, and cheesecake. Seating is plentiful on both the first and second floors, and the large space allows customers to stay late near Wangsimni Station. The coffee, including the americano, is disappointing.