I visited Sinsa Jeon for Korean fritters and makgeolli with honeycomb, but I was too full to finish the combination jeon, which is better for two or more people.
I found Nice Weather Market to be a very cool and funky store with a unique supermarket concept, offering a good curated selection of lifestyle products.
I finally visited the Starfield COEX Mall library, which was very busy but had an Arabica coffee shop where I enjoyed a Spanish latte and people-watched.