Originally Posted by mikesaidyes

I think that in four days, seeing five palaces is a waste of time as they all look the same.

The train takes just around 50 minutes from Incheon to Hongdae. 12 PM is the middle of the day (not 6 AM SE Asia arrivals, American/Europe arrivals haven't started), so it shouldn't take you too long to get out of the airport. I'd realistically expect a 2 or 2:30 hotel arrival. Drop bags and check in and out the door by 3-3:30.

A good subway app to download is Jihachul. As all the subway doors are marked by car and car door number, it tells you exactly where to stand to make your transfer the quickest, etc.

The only place to purchase T-Money cards inside the airport is at the GS 25 by Door 10 on the arrivals level. I tried at other 7-Eleven on the arrivals level (in Korean) and was told to go there. You cannot recharge with cash, but you should be able to make the initial purchase with card as it's rung as a normal transaction.

ATMs will take foreign cards, yes. Just make sure it has a Global Sticker. If you don't see one, you'll know it works by seeing "Foreign Card" as an option under the English menu.

To be honest, since you're arriving in the afternoon, I'd just check in and wait for Seoul Tower and sunset. Then, Seoul Tower at sunset (around 5 - need to plan to wait to get in and get up to the top) and explore Myeongdong at night. Myeongdong has a lot happening at night, but you just need to see it once.

The next morning, do a tour around Jongno area - go to the far east to Gwangjang Market, then swing back to Insadong and hop over to Gyeongbokgung Palace. On the way home, walk through Gwanghwamun Plaza and by the Cheonggyechon. Take a nap, rest, and then head tothe war museum and Itaewon for dinner. Itaewon used to be the seedy area, yes, but now it is SUPER trendy with Koreans and has TONS of international and cute restaurants in the area behind the Hamilton Hotel. The war museum is about a ten - fifteen minute walk west of the Itaewon area. From your hotel, take Line 4 to Samgakji (or a cheap taxi) and then the museum is there. After the museum, walk to Itaewon.

The next day: DMZ tour. Get back to the hotel and then maybe you can head to the national museum. It's also on Line 4 at Ichon. I actually hate museums, but still spent two hours there. It's huge.

That night: Head over to Jongno 3-Ga (around the area of subway exit 5) for dinner. It's a very traditional Korean neighborhood aka lots of old people, post work activity, all kinds of food (and there's a lot of guesthouses there so they're used to the random tourist).

The next day: Hop on Line 2 and head down to Jamsil/Gangnam just to see the area. Sports Complex stop has the stadium. There's a good mall at Samseong Station called Coex, for shopping. In the main Gangnam area, more shopping, shiny buildings and people (but nothing unusual for Tokyo of course).

Easier way to deal with bags: Take them with you when you check out and put them in a subway station locker. That way you don't waste time going back to the hotel. There's an airport bus from EVERYWHERE, so you can hop on where ever you are.