Seoul will host a two-day environmental festival at Gwangnaru Bicycle Park along the Han River, Saturday and Sunday, combining trash pickup with hands-on activities to mark Resource Circulation Day, observed Sept. 6, the city said. The event, called "Our Neighborhood Hangang Park Beautification: GREEN Hangang," invites participants to pick up litter, learn proper waste sorting and try upcycling crafts, including making cotton candy powered by pedaling a stationary bike and building musical instruments out of discarded materials. It builds on an ongoing citizen program in which the Gwangnaru Environmental Volunteer Corps has cleaned the park and removed invasive plants every Tuesday, Thursday and Saturday since April, drawing about 900 participants so far; those regular cleanups continue through November. A similar event tied to Environment Day in June drew 1,800 participants. Organizers said the festival also highlights the Han River's recovering ecosystem, which has recently seen the return of otters and other wildlife. The event runs across four zones. In Han River Guardians, participan