If you want to give your credit card some exercise, head out to COEX Convention and Exhibition Center in Gangnam-gu. Why not take a stroll along the riverfront and watch the sunset while you're here? It's also full of great shops and restaurants, so you can spend the afternoon having a wander. Splash some more cash at Starfield COEX Mall, Teheranno, and Hyundai Department Store Trade Center.
You can spend time browsing the exhibits at Kimchi Museum in Seoul. Amble around this culturally rich area's riverfront and enjoy its top-notch restaurants.