Namsangol Hanok Village
Besides being an interesting place, the Namsangol Hanok Village has another advantage over other sights in Seoul: It is open until 8 pm (10 pm from March to October). And it’s free, so there’s no reason not to visit this place.
This village is surrounded by some big buildings and was thus not easy to find. Namsangol is an open air museum, showing some traditional Korean houses including furniture. You can not go inside the houses but watch from the outside into them.
The five rebuilt houses reflect the architecture during the Joseon Dynasty and the people living there, from common people to the king. This area is also a playground where you can try out some traditional games like arrow throwing.
I guess during the warmer months there are more events at Namsangol. I also read that traditional wedding ceremonies are held there.