Yeouido Park is a great place to take great photographs, have a picnic or even jog/cycle around. The Cherry Blossom trees surrounded the street and its so mesmerizing to view with. Definitely worth a visit if you're in Seoul around early to mid-April. So many young and old people walked around here.
During spring all the cherry blossom trees bloom so nicely, it takes a hour or two to walk all the way from one side to another. This park also connected to the Hangang so visitors could enjoy the view of the river as well. The I Seoul U installation by the river also a great place for photos on a clear day.
The park is around 500 meters from Yeouido subway station. It is very nice place to walk and jogging. You can rent bicycle to go around the park.