The hidden gates are placed in locations that are difficult to observe from outside. They are used to carry supplies in and out, provide access for reinforcements, or allow soldiers to sneak out during battle. Sixteen hidden gates remain in the Namhan Mountain Fortress today, the most of any palace or fortress compound in Korea. Of these 11 are in the main wall, 4 are in Bongamseong, and one is in Hanbongseong.
Ammun no. 1 (hidden gate)
Hidden gates were located in areas the enemy forces had difficulty oberserving. The gates were small and hard to distinguish from the rest of the fortress. There is a total of 16 hidden gates at Namhansanseong (Namhan Mountain Fortress). While the other gates stuck out on the left or right of the fortress and could serve as battlements or observation posts, this did not. The tiny entranceway became wider as one entered the fortress.
Ammun no. 2 (hidden gate)
This gate was not built with the original fortress, but was added with the construction of Janggyeongsasinjiongseong (extended outer work).
Ammun no. 3 (hidden gate)
This gate was a main connection to the main fortress, Bongamseong (outer wall) and Hanbongseong (outer wall). Since there were no gates near the Dongjangdae (East command post), and the inclines were rather steep, this gate played the most prominent role of all secret gates. The gate is arched on both the inside and outside, and it width of 2.3m and height of 2.65m testify to its importance.
Ammun no. 4 (hidden gate)
A number of hidden gates were built around Namhansanseong (Namhan Mountain Fortress) in hard-to-observe, and they were small and virtually indistinguishable to the enemy. This gate was auxiliary to the Bukmun (North gate), and is a full kilometer away from Sangsacheong-dong in today's town of Hanam. The gate features a rainbow-shaped arch at the top.
Ammun no. 5 (hidden gate)
This gate was for access to the Yeonjubongongseong (extended outer work). The inner side of the gate featured a long stone wall so that the gate could be sealed for protection when the fortress was in use.
Ammun no. 6 (hidden gate)
This gate actually served as a sentry post facing the northwest. It was set up somewhat like a battlement to serve defensive purposes for the northwest portion of the fortress. On Jan. 23. 1637, the gate served to repel a Manchu attack in the middle of the night.
Ammun no. 7 (hidden gate)
This gate were located at the point were the fortress shifts in direction from the east/west to north/south and the opening faces the west. A hidden gate located where the fortress shifts direction provides an artificial bend and serves as an observation post while being virtually undetected from the outside.
Ammun no. 11 (hidden gate)
This gate, closest to the Dongmun (East gate) prohibited entry of wagons, so this gate apparently was used for pedestrians and wagons. When Catholics were being persecuted during the Joseon Dynasty, the corpses were carried through this gate, so it has become a pilgrimage site for Catholics.