The War Memorial of Korea (전쟁기념관)

Time describes it best:

Korea has been invaded about a gazillion times and this is the best place to learn about its troubled history, especially its relationships with its near neighbors. Though it calls itself a war memorial, this is really a huge military history museum ($3 admission), with tanks, planes and guns on display. Given that the peninsula is still technically at war with North Korea, this place seems very relevant. Take subway line 4 to Samgakji Station.

Hours: 09:30 ~ 18:00, Closed: Every Monday. If a holiday falls on a Monday, closed the next day.

Directions: 10 minutes by walking from Subway line 1, Namyeong Station

Address: 29 Itaewon-ro, Yongsan-gu, Seoul