Underground Heritage Documentation: the Case Study of Grotta Zinzulusa in Castro (Lecce-Italy)

3D documentation of the Underground Built Heritage (UBH) is always fundamental for knowledge, management, conservation, and enhancement of cultural heritage, but the challenges involved in documenting this kind of site are many and various, With the aim of providing an accurate and reliable representation of the surveyed area without employing time-consuming processes, Mobile Mapping Systems (MMSs) based on SLAM (Simultaneous Localization And Mapping) technology have now the potential to overcome these challenges, proving to be a useful alternative to traditional surveying techniques. The underground site of Grotta Zinzulusa in Castro (LE), Italy, is an anchialine cave system difficult to access and document due to its narrow passages, large rooms, and poor illumination. Within this case study, the effectiveness of using an MMS approach, employing the STONEX® X120GO SLAM Laser Scanner system, to document the cave system and integrates the data with those obtained from other traditional geomatics techniques, such as UAS (Uncrewed Aerial System) and TLS (Terrestrial Laser Scanning) surveys, has been proved. The study aims to define the best practices and operational methodologies for enhancing the speediness, usability, and cost-effectiveness of using MMSs in underground settings for 3D documentation of heritage sites to provide metrically correct and accurate products for researchers, scientists, and the wider public.