After hiking yesterday in Gunpo, I also briefly visited a market there. There were various stalls and shops selling fresh fruits, veggies, meat, seafood, etc. This is similar to farmer’s markets in America. Korea does have supermarkets such as Homeplus, e-mart, and Lotte Mart that are similar to Wal-Mart or HyVee. However the Korean outdoor markets sell fresher foods for a much better price.
Also, because of the MERS outbreak in South Korea, it’s important to always wear a mask when using public transport. Of course, wash your hands frequently and cover your coughing/sneezing (which you should always do, even if there isn’t an outbreak). Stay safe!