Many who go to Dunsan-dong at night end up in this beer bar at some point during the evening, or early morning. It's a decent walk here from a metro station.
From City Hall station, take Exit 2 and walk to the Galleria department store. Beside the large McDonald's sign, cross the street and walk down the road opposite the sign. At the end of the street turn right. The bar is down the street on your left.