Seoul Forest is located on former hunting grounds, and was opened as an urban island park in 2005. It’s a lovely spot for a run, with some nice variety. The park is divided into four ‘sections’: Culture and Art Park, Eco-Forest, Experiential Learning, and Marsh Plants Gardens. There are paths all around the park and a small lake, which can add up to 3-4 km within the park. A nice 1 km straight shot is to follow Apple Tree Rd. (entrance 16 on the map) to Ginkgo Rd., which is a lovely, shaded canopy with blossoms and very pretty in autumn. Also, look for Cherry Tree Rd. into the Eco Forest and loop around the small pond. This brochure has excellent information and a map. A nice spot to see cherry blossoms, in season!
Another option is to use the ‘bike road‘, which runs along the western perimeter of the park, from the Eungbong Bridge, south through the park, and then along the water, through several parks to the Jamsil Bridge — nearly 8 km one-way. The bike road also connects to the Hangang Riverside and the Jungnangcheon Riveside.