I was in Seoul (Millenium Hotel) 2 weeks ago for a 6 day layover. For shopping go to the Namdaemun Market, it's a few blocks from the Millenium (if that's were you stay). It's one of the largest outdoor markets in Seoul. I also did the DMZ tour through the hotel. We went to Tunnel #3, it's the one you walk into, It's much better than the one with the tram ride. It was an amazing tour and I highly recommend it. Don't forget to bring your passport with you on the tour, it's required to enter the DMZ. Have fun!