This free museum covers the Korean history, culture, and Korean war. It’s a must see if you like history. They have a nice collection of aircraft, tanks, artilleries, uniforms and objects from the Korean War. The museum also has temporary exhibitions (entrance not free). Check out their website to see what is currently exposed. The museum is walking distance from Itaewon.
29 Itaewon-ro, Namyeong-dong, Yongsan-gu, Seoul, South Korea