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
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.
Live concerts everyday, clubs, bars and unique fashion stores..