Just when you thought you've seen all the historical artifacts a smaller country like Korea could have, there's another museum at the next palace with a whole new selection and something special to make it stand out.
As mentioned before, the National Folk Museum is located in Gyeongbokgung Palace and admission is free. There is an English audio guide for 1000 won, which for those not in a rush would help really explain the exhibits. I don't know if it covers the outside buildings. There are also guided tours at 10:30 and 14:30.
The museum is open daily (except Tuesdays). 9:00-18:00 March-May, September-October; 9:00-18:30 June-August; 9:00-17:00 November-February. It stays open until 19:00 on Saturdays, Sundays, and holidays May-August.
To get to the museum, use exit 5 at Gyeongbokgung Station (Line 3). The closest museum is the National Palace Museum, followed by the palace; the Folk Museum is at the back. The museum's English-language website is pretty good.