They have almost everything you would ever want and are a great place to kill time.
Like the one at Express Bus Terminal in Seoul, this store has many options.
One nice thing about being a foreigner in Korea is the Global Tax Free shopping. When I'm shopping at more established brand stores (like department stores and most makeup stores), I always ask for "Global Tax Free."
Read more about Global Tax Free shopping and food courts.
Even if I know I didn't spend enough to warrant it being worth my effort or if I am not sure they do it, I ask for it anyway. You get a special receipt and then have to go to the customer service counter to get a special form. Since I rarely carry my passport with me, I just tell them I don't have it at the moment. Then, when you get back to your hotel, just fill out the form with your information. When you get to the airport, follow the signs to the Global Tax Free counter and turn in all of your receipts and show them your passport and ticket and then you get all your tax back.
I really like going to food courts at Korean department stores. Yes, the products are a little overpriced, but you usually find pretty high-quality, very visually-appealing items with character.
At first the food floor may be slightly overwhelming, there are groceries, wine shops, sit-down restaurants, Korean restaurants, Chinese restaurants, Western Restaurants, Japanese restaurants, bakeries, bingsu stalls, cafes, etc. etc.
The experience of it all is totally worth it. It allows you to get a glimpse of all the current food trends in Korea in one confined location.
Steamed bread buns are a favorite of mine. They are portable, comforting, and flavorful.
While I was waiting in the Shinsegae Department Store in Busan for a friend, I stumbled across this green tea steamed bun I the shape of a pig. It was filled with pat (red bean paste).
It was expensive (3,000KRW), but it was so cute that I couldn't resist it!
I'm sure you can find it some other places, too.
Fun fact: The Shinsegae Centum City Department Store was recognized by Guinness Book of World Records when it opened as the largest shopping complex in the world. It houses a lot more than just shopping.
Floors 11-14: Golf Driving Range
Floor 10: Sports Club and Spa
Floor 5: Book Store
Floor 4: Ice Rink
Floor 1-3: Spa Land
Location: Centum City (Busan Subway Line #2)