If you saw Seong San and Seopjikoji in the morning, I suggest you go to the lush Bija Forest! It will clear your head and you'll be able to take in some clean air. It only took us about 30 min. from Seopjikoji by car. :)
Address:
3161-1 Pyeongdae-ri, Gujwa-eup (55 Bijasup-gil)
Jeju-si, Jeju-do
제주특별자치도 제주시 구좌읍 평대리 3164-1
Bija is a kind of plant - Torreya nucifera in English. According to Wikipedia, the seeds are used for medicine and the tree trunks for furniture like little tables and baduk boards.
Other kinds of plants in the forest
This one actually looks like sesame, and made me crave samgyeopsal :P
These two 'love trees' surprisingly wrapped around themselvses and grew together, not impeding each other's development. How sweet, they must really like each other. :)
See you again, Jeju! 8D