(It's in a building called "First Tower". I'm sure if you Naver search First Tower in Korean you'll find it.)
It's got a wide selection of restaurants (that seem more like "booths") to choose from. My favorite "restaurant" is TomaTillo.
This place satisifies my hunger for Mexican food as they have a good selection of dishes.
However, I usually get the burrito set/combo.
A spicy burrito plus chili-cheese-nachos sure hits the spot!