J. W.
Google
Beautiful park, great walk. Full of jungle crows and other wonderful island wildlife. We even ran into a deer when we were there.
Didn't get a chance to see the craters, but I'd love to go back and try to see them next time.
Easy to get to from Jeju city, we took a taxi which cost 17,000krw, we hiked the whole 10km trail and were easily able to get another taxi on the other side using the kakao taxi service. The bus also goes there and seems to run pretty often if you prefer public transportation.
One side of the park entrance has food trucks and public parking. I'm not sure I saw any on the side we started from, but the parking is likely there as well, but double check if you're driving.