The fortress is impressive, the gates certainly stand out, and the view of Seoul from the South is stunning on a clear day. The fortress today is primarily from 1624, but fortifications have been located here since Baekje and Silla in the 7th century.

The fortress played a major role during the Joseon dynasty, acting as the protective barrier of Southern Seoul, and more importantly as a temporary palace and headquarters for the king in times of peril. (In which purpose it was used on occasion) Namhansanseong itself is one of the better preserved fortresses in Korea. The walls are higher than most, while many of the gates are particularly formidable. The primary rebuilding phase is largely a response to the Japanese invasion of 1592, and the probability of Manchu incursions (which did occur in the 1630's).

I did notice one section of the wall was being almost completely rebuilt, but for the most part, the fortress is highly authentic. (Probably more 'original' than Hwaseong Fortress). The outer wall fortress, which was taken by the Manchu forces is largely in ruins.

There are a select few original wooden buildings, but most have been rebuilt or restored over the centuries. The Temporary Palace is the primary focus for restoration. Getting to the fortress is not particularly hard, there is a (somewhat) nearby subway. Buses also drop off visitors within the lower interior of the fortifications. This is one of the representative fortresses of Korea. If you enjoyed Hwaseong, you will surely enjoy Namhansanseong as well. One plus is the beautiful location, the old pine trees are numerous and the entire area is a provincial park.

Update: I revisited this fortress in order to hike the entirety of the wall and visit the outer portions. After 4-5 hours of hiking I accomplished this, though not without great effort and exhaustion! I have now visited all gates, and secret gates, and most Buddhist temples. It should be known before attempting any circumference hike that there are extremely steep sections, heat is an important factor to consider, and the Outer fortifications are primitive. What I mean by primitive is that facilities are non-existent, and signs for hikers are recent additions or not present. This portion of the fortress is in ruins and collapsing, this is likely because of two reasons: the outer fortifications are very hard to maintain based on location and this portion of the fortress saw some of the worst damage during the Manchu Invasion of Joseon.