Following are links to Strava rides in the Seoul and Gyeonggi regions, and brief descriptions of each course.
NamBuk: One of the most common rides within Seoul, this route takes you over Namsan first and then on to Bugaksan. Neither climb is terribly long or difficult for experienced cycling, but they do require some good effort. The views from Namsan are quite famous and the views from Bugaksan Palgakjang are stunning.
Namhansanseong (NHSS): This is one of the most popular routes for cyclists around Seoul. Most of the ride is flat and easy going along the Han River before hitting the mountain. The two sides of NHSS have completely different characteristics. One side is long and gradual with an upward pitch at the end; the other side is half the length and regularly over 7% with a little stretch for some recovery near the end before the finish. Be careful on the downhill on this side, as it is quite technical and buses coming up often cross the center line.
Yangpyeong Yangsu Station – Seoul via NHSS: This route is a pretty tough course that includes seven climbs. The first three are rather steep, though short. The biggest elevation gain comes at Yumyeong-san and then finishes with the long, slow climb at Namhansanseong before going back to Seoul. Great route for those who like difficult rides with a lot of elevation gain.
The Seoul Trifecta: This is a route that includes the three most common climbs close to Seoul: Namsan and Bugaksan in the city, and Namhansanseong a little southeast of Seoul. It can be a fairly tiresome route depending on pacing, but manageable for any strong rider. Much of the ride is on the Han River which is flat, and none of the climbs are terribly difficult.
Songchoo 3 Hills: This is a nice medium length route with a couple short steep hills. The ride out does go along some narrow, busy roads with a lot of trucks, and the ride back in to Seoul is a bit busy as well. But otherwise a good medium length ride with elevation gain.
Bunwonli: This area near NHSS is full of rolling hills along the Han River. It’s a great ride for putting in strong, hard efforts or just enjoying some really nice scenery. It’s easy to combine with NHSS to make for a long, tough ride. The linked route includes NHSS.
NHSS-Bunwonli-Hanggeum-ri-NHSS – Long tough ride with good climbing and rollers.
Seoul – Gapyeong: I do this route once each year because I enjoy it so much. Depending on the starting point in Seoul the route is 100-120km and includes two small climbs and two larger climbs, including Homyeon-san, which is excellent.
Ganghwa Island: This loop from Seoul to Ganghwa-do is a long, mostly flat route. Some people really seem to enjoy Ganghwa Island, but I personally find it rather unimpressive. But, for a long ride from Seoul that will take you along part of the west coast, it’s not a bad route overall.
Seoul to Yeongpyeong 5 Climbs: This route is long and really tough. There are five total climbs, the largest of which is the excellent Yumyeong-san. It’s simple enough to shorten this route by taking the Gyeongui-Jungang Line on weekends either to or from Yangpyeong.