Asia - What to do in Seoul?

I have a nine hour lay over in Seoul. What sites or attractions could I see in that time? What would be the least expensive way to travel to them? I have never been to South Korea, So I would like to see something interesting while I am there. Historical, unusual or exciting. Not shopping or eating. Thank You in advance.

Is that a 9 hour layover in ICN? Assuming so, then travel to/from the city will take about 1 hour + in each direction depending on traffic. Cheapest way into town is the KAL Airport Limousine (which is actually a bus). Once in town, I'd take the Seoul City Tour Bus (http://www.seoulcitybus.com/eng/subB_D04.htm)which takes about 2 hours and allows you to hop-off at each stop along the way and then hop-on the next bus that is 30 minutes behind, so you can selectively pick a few places to explore. Cost is approx KRW10,000 depending on which route you take.