There are some royal palaces in the middle of Seoul city, and if you want to visit there I'll send you some English written guides for you. There are 5 major palaces that are more than 500 years old, and a lot of foreigners visit there.
Famous restaurants are usually full of people, and most of the time reservation is required. But if you avoid the peak time like 11:00AM-14:00PM and 17:00PM-19:00PM, then it will be easier. I'll ask my friends to recommend really good places and then send them to you :)
If you planned to come here alone, please ask your friends to come together. Hotels are expensive to stay for only one person, and taxis also.