In recent years, Unmanned Aerial Vehicles (UAVs) have emerged as a promising solution to perform critical tasks in a vast range of industrial applications and for monitoring large critical infrastructures. Bridge inspection, as one of them, is essential to ensure the structural integrity and safety of these vital infrastructures. By exploiting the advantages of the UAVs, it is possible to create a more safe and automated solution compared to the traditional inspection methods that often involve manual labor, time-consuming processes and potential risks to human inspectors. In this context, one of the most challenging problems is represented by the localization of the Inspector UAV beneath the bridge because of the limited or completely absent satellite visibility.