A decorated and carved wooden door of the late Byzantine period (14th Century), which belongs to the Dionysiou Monastery in Mount Athos, Greece, constitutes an important relic of valuable technological information due to its construction technology and history. Seventeen (17) samples detached from the door are studied using optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray analysis (SEM-EDX), and micro-Raman and FTIR spectroscopy. The following materials are identified in the cross sections of the door samples using micro-Raman spectroscopy: orpiment, lead white, red lead, red ochre, cinnabar, carbon black, gypsum, anhydrite, and calcite, and an organic colourant of the indigoid family. SEM-EDX studies supported to the aforementioned Raman results. Interestingly, a combination of inorganic and organic colourants was detected. The main goals of this particular study were to: (a) reveal the colour palette and materials, (b) identify the type of varnish and its condition, and (c) contribute to future restoration processes and aid conservators in selecting compatible restoration materials.