This study examines an application of Augmented Reality technology (AR) for Korean Cultural Traditional Buildings, specifically, the Namdaemun Gate, “National Treasure No 1” of the Republic of Korea. Unfortunately, in February 2008, the Namdaemun Gate burned down, despite the efforts of many firemen, as the main difficulty was getting the fire under control without any structural knowledge of the wooden building. Hence, with the great advances in digital technology, an application of virtual technical information to traditional buildings is needed, and the new technology of AR offers many such advantages for digital architectural design and construction fields. While AR is already being considered as new design approach for architecture, outdoor AR is another practical application that can take advantage of new wearable computer equipment (Head-mounted display also know as HMD, position and orientation sensors, and mobile computing) to superimpose virtual graphics of traditional buildings (in this case, Namdaemun Gate) in a real outdoor scene. Plus, outdoor AR also allows the user to move freely around and inside a 3D virtual construction, thereby offering important training opportunities, for example, specific structural information in the case of firemen and mission planning in the case of a real-life emergency. In this example, the proposed outdoor AR system is expected to provide important educational information on traditional wooden building for architects, archaeologists, and engineers, while also assisting firemen to protect such special buildings.