From Incheon station Take the Seoul subway Line 1 in direction Yongsan(rapid train). At Guro Station transfer to line 5 direction Banghwa. Go two stops on Line 5 to Yeongdeung Po-Gu Office station. Transfer to the 2 Line direction City Hall and go three stops to Hongik University Station. Get off at Hongik exit 5 and you'll be in the heart of Hongdae area. Hope this helps!