Seoul Science Park is a peaceful place to take a break. Have a picnic, throw a ball around or just lie on the grass and shut your eyes for a while.
Seoul Science Park is free to visit, so you'll be able to give your bank card a break for a while. After you've finished exploring this recreation and green space in the leafy neighborhood of Nakseongdae-dong, have a look at nearby National Museum of Korea, N Seoul Tower and Namsan Park as well.