Here are my suggestions of places to visit in Seoul, to celebrate National Liberation Day:
Situated by Yongsan military base, in between Noksapyeong and Samgakji stations, this military history museum and memorial is free to enter, and offers an up-close look at machines, vehicles and weapons that were used in the Korean War, World War II and the Vietnem War.
2. Seodaemun Prison (Link coming soon)
Covering a vast area of peaceful, grassy grounds, Seoul National Cemetary is a good place to go to pay your respects to those who fought and died in the Korean Independence Movement and the Korean War. Dongjak station, exit 8.
4. Seoul Museum of History (Link coming soon)
Close to Gyeonghuigung Palace in Jongno, Seoul Museum of History contains permanent exhibits showing what Seoul was like under Japanese control, as well as of course many other exhibits showing different periods in Seoul's history.
Even if you don't have time to visit any of these places this weekend, make sure you visit them another time while you're in Seoul, because they all offer an eye-opening and educational insight into how modern day South Korea came into being.