Ammun (Korean: 암문) is a type of gate in traditional Korean architecture that was built without intentionally building a gate tower in the castle walls. It was usually built in a remote or deep place so that the general public or enemies would not know about it, and it was used to secretly transport supplies.^[1]

It is built in the form of a hole in the wall without a gate tower. It was built to allow passage when the enemy blocks the main gate in case of emergency. There are a total of 9 secret gates in Hanyangdoseong.^[2]