Immigration will normally process a short term extension of your visa (up to 15 days), to allow you to do such things as visit friends or sightsee or clean up personal business such as bank accounts, utilities disconnects, etc or if in fact you couldn’t book a flight out soon enough. Simply appear at anytime between 30 days before and up to the day before the expiration of your visa and fill out an application form to extend your sojurn and have it duly processed. There is no fee to do this. In the brief interview they will ask you things like “Have you booked your departure flight? Why do you want an extension?” Pretty painless process.
Recommendation: If you know in advance you want a little extra time in Korea before you take off – get it done earlier than later. The penalties for overstaying your visa can add up quickly (by the day).
Failure to have your paperwork in order can result in fines of up to 100,000 won per day that you are over your visa. Don’t lose your hard-earned cash to a lack of planning.