ICN airport – Seoul/Incheon Korea 12-hr layover

Arrived ICN today at 6:40 AM after a 14-hr 28-minute flight from Atlanta.
My connecting flight to Chiang Mai doesn't leave till 6:45PM.
WHAT TO DO???
Well it turns out that the airport and Korea are offering "Korea Free transit tours". That's to help travelers with some free time get to do some sightseeing for FREE - in the hopes you will have a good time and come back for a visit to Korea. They have 6 tours - travel time varying from 1-hr to 6-hr.
I enjoyed the 3.3-hr tour.
Now, with 3-hrs before checkin, I think a 2-hr NAP might be in order....