Haneul Park is one of 5 small parks located within World Cup Stadium Park. Most notably, it was a landfill for 15 years before being converted into a park and stadium for the 2002 World Cup that Korea co-hosted with Japan.
While I enjoy the parks in Seoul and am ever grateful that they are there, I typically find them overcrowded and tend to avoid the more popular ones. Haneul Park was no different. In the fall they typically hold an Eoksae Festival, or Silver Grass Festival. It is popular and filled with many groups and couples. While I was off-put at first, once you are into the park there are so many mazes and corners off of the main trail that you can easily find yourself lost and alone.
Simply put, it was gorgeous and peaceful.
For more information, you can visit Korea's tourism website.