I just booked for three nights in mid December. In spite of what people say about not being for tourists, the website says it's right next to a metro station ^^ and a shopping mall (which I assume is open):
http://www.ifcmallseoul.com/eng/jsp/store/mallMap.do
The Hilton Grand has a great rate for points + cash but tripadvisor makes it sound especially awful; the Millenium Hilton seems better but for 30k KRW difference, I'd like to try a brand new Conrad.