Pakito is probably my favorite Spanish restaurant in Seoul (and also the furthest one from my place as it had to be). I like it because it feels more like eating in Spain than other dining restaurants thanks to its "taberna" style.
The owner, who speaks good Spanish and cooks like one, makes very tasty Spanish omelettes (tortilla), and a great oven chicken (pollo a la catalana). Other tapas were also amazing, and he is one of the few places that I see actually serving tapa sized tapas (not huge ones for 20,000w but smaller individual portions for 4,000w or more).
The place is very cozy, so if you are a big party, make sure to be there from 6 at their opening time. We also tried the sangria and it was well mixed. If it wasn't so far away, I would definitely spend more time there!