This mountain is located in the heart of the city and is home to the N-Seoul Tower. It is easily accessible from numerous subway stations surrounding the park and has a combination of sneaker-friendly hiking trails, paved stairways, and a paved walking lane that runs alongside the road. The view at the top is worth the short hike up, and you can pay some money to ascend the tower itself, if you wish. The walls at the top are covered in locks of various colours, sizes, and shapes, and the vast majority are probably put there by couples as a romantic gesture. If you like having ice cream, beer, or a bucket of popcorn when you get to the top of a mountain, this is the hike for you. My favourite part was seeing the park, sculptures, and crenellations on the way up.
Difficulty: Very Easy - 1/5 Peak: 262 m TL;DR: Touristy, very short, and one of those things you do to say that you've done it.
Ansan
There are many ways to ascend the mountains in Seoul, but we stumbled upon a very interesting one with Ansan. After leaving the subway station, we found ourselves alone in an abandoned neighbourhood. Abandoned except for the cats, of course. The broken buildings and quiet streets made for a memorable and eerie start to the hike. The trails leading to the summit were a mixture of boardwalks and wide, well-established paths with large, friendly stone stairways. And at the top, there was a railed-in viewing area that afforded a dazzling view of the city and the Han River. This short, scenic hike is a must-do, in my opinion.
Difficulty: Easy - 2/5 Peak: 296 m TL;DR: It's short and sweet and you'll want to sit and drink in the view from the top all day long.
Suraksan
Oh, boy. I have a feeling that this mountain is going to be my favourite for a long while. The trails were beautiful and not too crowded, there was a Buddhist temple along the way, and the view from the peak was simply breathtaking. Trevor and I explored a little more than most people seemed to; we climbed on top of trail-side boulders and went straight up rock faces instead of taking the more circuitous routes. The trail was a combination of paved roads, stone staircases, dirt paths, wooden staircases, and the last leg was a series of steep, rocky scrambles that required the use of your hands. There were occasional handrails made of steel cable to grab on to as well. We began our descent as the sun started setting and witnessed the mountain bathed in pinkish gold light.
Difficulty: Moderate - 3/5 Peak: 638 m TL;DR: It was magical. You should go.
Seoraksan National Park
This park and these mountains have been talked about ad nauseam by myriad people before me, so I'll be brief. We did two hikes over two days. Day 1 was the hike to Towangseong Falls Observatory, which took about two hours round trip. The guide (in the gallery below) was accurate in its difficulty rating, I think. But the "hike" to the observatory was actually just a tediously long staircase. At the top, we were surrounded by mountains and two (frozen) waterfalls. I think this hike would be better in the summer, since the waterfalls wouldn't be frozen, but it was refreshing to be outside and the views were still stunning even in the winter.
Difficulty: Good leg workout - 3/5 Peak: N/A TL;DR: Worth checking out if you're in Seoraksan.
On Day 2, we went all the way to Ulsanbawi Rock. The hike to Heundeulbawi Rock was thoroughly enjoyable, beginning with an easy riverside stroll and building up to a proper hike over some stone staircases and dirt paths. The 1.0 km to Ulsanbawi, however, was... arduous. It was entirely stairs. It began with stone stairs on a path amongst the trees and ended with man-made stairs that hugged the mountainside and afforded a thrilling and dizzying view straight down. The stairs went on for a very long time, so we had to take several breaks to catch our breath. The view at the top was absolutely breathtaking in all the right ways. We could see the ocean stretching far away and the city of Sokcho. But, unfortunately, the icy wind was breathtaking in all the wrong ways. This is a hike that I don't recommend in winter, simply because you're going to be blasted off-balance by wind that cuts through your layers and freezes any exposed skin. The one good thing about the strong winds that day was that we could hear the mountain singing on the way down. When the wind blows over the mountain, the rocks make low, musical sounds similar to when you blow air over the mouth of a bottle. I'm excited to return in the summertime for a few days to tackle the actual Seoraksan summit (1708m) and find out more about about Geumganggul Cave. :)
Difficulty: StairMaster for 1 hour straight - 5/5 Peak: 817 m TL;DR: Rivers and waterfalls and singing mountains, oh my. This place has it all and I highly recommend going.