in case of that your 'play' meant 'have fun'. 1. Gangnam (gangman station line 2) good for shopping, crowded like crazy with young people, known for its skyscrappers, fashion and business 2. Myeongdong cheap and interesting food, beauty stuff and cloths. more crowded than Gangnam. the first Catholic church in Korean history is there too. 3. Insadong (anguk station line 3) traditional stores and cafes. as Peachey said, there is a huge instruments market too. 4. Hongdae Live concerts everyday, clubs, bars and unique fashion stores..

Play music? Good question... If you're confident in your Korean, go to Nagwon (it's a music superstore, upstairs in that huge grey building straddling the street) near Insa-dong and ask the music staff there. They may give the best advice! Perhaps try around the university areas? They're very vibrant places.