Seoul Grand Park sits at the foot of Mt. Cheonggye in Gwacheon, just south of the Seoul city limits and reachable on metro line 4 (Seoul Grand Park station). It is the country's largest park complex, combining Korea's biggest zoo with a botanical garden, Seoul Land amusement park, hiking trails, a campground, and the National Museum of Modern and Contemporary Art (MMCA).
The zoo alone covers a full day if you let it — over 3,000 animals across themed zones. On a hillside overlooking the central pens, the botanical garden houses more than 1,100 species of tropical plants, cacti, orchids, and ferns under a series of glass domes. The MMCA, in a separate compound, is worth a visit in its own right for anyone interested in Korean contemporary art.