Having driven in Seoul, I would advise against driving. Korean drivers strike me as being extremely aggressive, making frequent lane changes, and turning a four-lane road into a six-lane road. I never observed a "flow" of traffic, or the sometimes playful interaction that can be found in Southern Europe; in Seoul, it's pure aggression, and at every traffic light/merge situation you're inches away from making contact with another car. In addition, few road signs are based on pictorials, so you will get lost unless you are able to read Korean. At the same time, cabs are very cheap, and I've hired drivers for as little as 15k KRW per hour (black cab). So I'd say, driving is just not worth the hassle. Only exception: I would not have any concerns about driving on Jeju island.