This looks to be a promising pool hall in the Shinchon area. I haven't been here yet, so can't give you exact directions or details, but the address is below.
서울 서대문구 대현동 101-7 혜우빌딩 1층 타겟포켓볼
Seoul, Seodaemun-gu, Daehyeon-dong, 101-7 Hyewoo Building 1st floor
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