Noeul Park, Seoul Olympic Stadium and Nanji Park
These parks are all located in one area, alongside Haneul park. I arrived in this park area around 7:30 AM and by the time I was done visiting all of them I clocked in around 1 PM. I was taking a lot of photos along the way so I may have taken longer than usual. If you wanted to, you could literally spend your whole day around the parks. Noeul Park and Nanji Park have camping areas where you can setup tents and just chill out.