Great Offline Subway Map
Im living in Seoul for the summer (from the US) and have tried most of the offline maps to try and get around the city. I ended up using this one the most. It was very helpful and easy to use. Its very handy to have a familiar map to look up the names of the stops here when youre in the station or on a subway (rather than have to figure out where you are on the map at a particular station or subway). Anyway I highly recommend this to anyone using the subways in Seoul.
mkoye about
Seoul Metro Subway Map