My two favorite hotels in Seoul are the Westin and the Grand Hotel located downtown.  Seoul has a great subway system that gets you everywhere whether you are going to visit the Olympic Stadium south or downtown or up north to Independence Gate and Puk'Ansan National Park.  Make sure you hit the Namsan Tower (similar to Space Needle) for a great view of the city.  After a day of sightseeing hit the one of the Seoul's great restaurants for an authentic Korean Barbecue and the local brew.