Three arched portals dissect the south wall of the Gallery of NTU History's central exhibition hall. The arches to the left and right serve as passageways connecting the entrance hall to the central exhibition hall, while the central arch is fitted witha transparentglass doorway that leads to a secret location unknown to even the most senior staff at NTU.

Beyond the mystery door, visitors are invited to descend a winding stairway to a confined space just below the gallery's central exhibition hall. An intermediate floor, this once-forgotten niche of the NTU campus began housing a book repository in 1932 when the central exhibition hall was still a reading room of the previous NTU Library.

Back then, students were prohibited from browsing the library's book shelves,and a book checkout and return counter blocked the central arch that led to the repository. Accessible only by the cramped stairs, the repository below was once a restricted area. Following the construction of the new Main Library, however, the repository was relegated to an ordinarystorage space, andultimately, a wall was built to seal off the chamber behind the archway.

Following the opening of the history gallery in 2005, the wall was torn down and the old repository resurrected. Now a unique corner of the Gallery of NTU History, the space has beentemporarily transformedintothe NTU Photography Club's semester-end exhibition venue, drawing over 900 visitors.