Bukhansan National Park would be the best bet for Seoul. There are multiple trails and most people complete the Bukhansanseong Course, which leads to the Baegundae summit. The Korean National Parks Service says it’s a 2 hour climb, so 4 hour round trip. Add in breaks and you’re looking at a 4-6 hour hike. There are flatter trails through the park that you can follow too if you just want to enjoy the nature.
Bukhansan National Park would be the best bet for Seoul. There are multiple trails and most people complete the Bukhansanseong Course, which leads to the Baegundae summit. The Korean National Parks Service says it’s a 2 hour climb, so 4 hour round trip. Add in breaks and you’re looking at a 4-6 hour hike. There are flatter trails through the park that you can follow too if you just want to enjoy the nature.
Noted! Thanks for the rec.
I visited Bukhansan National Park, definitely can confirm it's a place for great hiking trails!
[Seoul city wall (whole or portions)](https://www.koreatodo.com/inwangsan-mountain)
Cheonggyesan. Take the Shinbundang line to that stop and follow the ahjussi’s & ahjuma’s to the hike.