The War Memorial of Korea in Yongsan, near Itaewon, is a large outdoor and indoor museum covering Korea's military history from ancient times to the present. The outdoor grounds display tanks, aircraft, artillery pieces, and naval vessels; the indoor galleries cover the Japanese occupation, the Korean War, and post-war development in considerable detail. The Korean War section is comprehensive and includes English captions throughout.
This is not a cheerful museum, but it's an important one for understanding the city around it. The bronze statues outside, particularly the two soldiers embracing — one from the South, one from the North — are among the most emotionally direct public sculptures in Seoul. Admission is free. Allow two to three hours.