Seoul is a vast city, mixing tradition and modernity. Because of its size, you’ll need to take transportation to go around and see most of the town. It is a busy capital.
In South Korea, people go out a lot, either to go to restaurants, cafes, or to go out or to study. Koreans live a lot outside of their home. So even if this city has a very clean and peaceful vibe overall, you still might feel the need to find calmer and less dense spaces. Nature has this effect, and the capital offers many nice parks or walks where you can take a break from urban life.
Here are some places I really enjoyed for this purpose!