Executive Summary Railway tunnel inspections have been mainly undertaken in the traditional manner, which does not provide very reliable data and it is time consuming. Therefore, alternative methods need to be developed in order to have more quality in data collected from the tunnel inspections. The current project aims to design and construct an optical-thermal camera rig for railway tunnel inspec-tion. This system is therefore to supplement the visual and manual procedure, being more effective and contributing to the maintenance of the railway sector. For the purpose of analysing the performance of the proposed system, several tests were carried out in one of the GCU labs in order to determine the quality of the imaging. At the same time, throughout these months of work, several iterations had to be done, having even the requirements on the GUI Software Development change, from a video display to an image display that could be continuously refreshed due to the file type of the camera’s output. The most recent iteration was able to achieve the established goal, presenting the user with a window with the two image displays and all the necessary buttons performing the requested action to display the different images from the 5 pairs of cameras. Then, the first mechanical tests on the geometry showed some inconsistencies, where for some cases the quality of the imaging was poor, not having enough overlap between the data obtained by each camera, whereas for other cases it was possible to collect great images. Thus, the system design needed to be en-hanced. The final design showed data with excellent quality. This results thus indicate that the system is capable to perform the data collection from the actual tunnel for condition monitoring.