Jirisan National Park straddles several regions and different points of departure are possible depending on where you want to go. The hiking trails are not accessible year round for climatic reasons.
From Cheonwangbong, the summit of Jirisan, the view of the sea of clouds is breathtaking, but access is difficult if you are alone. I strongly recommend you hire a guide.
In the autumn, I found the (very long) hike to Piagol particularly beautiful, when the maple trees turn red both in the valleys and on the mountainsides. During the summer, shorter hikes of about two hours lead to spectacular landscapes.
The trails in the heart of the forest go through villages, which gives you a glimpse of another way of life, far from the tumult of the major Korean cities.