In this paper, a specialist examination of the tunnel Sveta Tri Kralja on the Zagreb-Macelj highway is elaborated. The introductory part defines what a tunnel is, states their general division, the purpose of their construction and the reason for their decay. The importance of conducting a specialist visual examination was also emphasized. Before elaborating the topic, it is shown of which parts the construction of the tunnel is made and what is their role. Furthermore, it is defined what is actually a specialist visual examination, which is the goal of its implementation, its implementation is described in detail, the necessary equipment for implementation and a description of investigative works used as a supplement to it. Tunnel Sv. Tri Kralja is located in space in a way that shows its macrolocation and microlocation. Also, a detailed technical description is given for the tunnel. Prior to the implementation of the visual inspection, a detailed inspection plan was made. During the visual inspection, all observed damages were photo-documented and they are presented and briefly described in this paper. The damages were analyzed in detail and the causes of their occurrence were investigated. Furthermore, the current condition of the secondary tunnel lining was assessed and a repair method was proposed for each type of damage. Finally, based on the perceived importance of conducting a specialist visual inspection, analysis of the observed damage during its implementation and investigated the causes of their occurrence, a conclusion was drawn.