Gunnar Caya
SerpAPI
Hallasan National Park is incredible. Easily my favorite of the 8 other Korean National Parks I've seen so far. The highlight of course is hiking all the way to the summit of Hallasan, where, if you're lucky like I was, you'll get to see a sea of clouds below you as you stare down at a beautiful, sleeping volcano. But regardless of the weather and time of year, Hallasan is a beautiful sight to see. If you have the opportunity (and you're able to score a permit to hike to the summit via the Gwaneumsa or Seongpanak trails), you should totally do it.
The hike to the peak is awesome, probably the most enjoyable one I've done in Korea. Getting there isn't exactly easy, but if you're in at least decent physical condition it shouldn't be too hard. It took me a little less than 6.5 hours to get to the top and back down, but I've heard some people say it took them around 9 hours. Either way, a hike to the summit is an all-day affair, so start as early as your permit will allow you to. I started at around 9:30am on the Gwaneumsa Trail and reached the final shelter at 11:40am, only 20 minutes before they stopped letting people continue to the summit. A 10am-12pm permit probably won't leave you enough time unless you move at a breakneck speed and don't stop for pictures or to catch your breath a couple times.
Even if you don't make it to the summit, it's still an awesome sight, and if you take the Gwaneumsa Trail, the views along the way will be absolutely spectacular. Of course the best views are all beyond the final shelter on either course, so do try to make it there before last call. But regardless, this is perhaps my favorite thing I've done during my time in Korea. Wholeheartedly recommend