Balancing heritage conservation and public accessibility in hypogeal sites: environmental monitoring of occupancy scenarios

Hypogeal sites represent unique cases of cultural heritage, especially when they feature decorative elements such as graffiti, frescoes, or bas-reliefs. Preserving these sites relies significantly on maintaining stable internal microclimatic conditions, which are often isolated from external environmental influences. However, visitor presence can disrupt this delicate balance by altering key parameters like temperature, relative humidity, and carbon dioxide levels, particularly in small-sized spaces. As a result, making such sites accessible for tourism requires a careful assessment of scenarios that balance visitor numbers, visit duration and conditions, in view of people wellbeing and heritage conservation. This paper explores the findings from environmental monitoring at the Crypt of San Leonardo in Monopoli, Southern Italy, a small yet historically significant site enriched with 13th-century religious paintings and inscriptions. Starting from the acquisition of microclimatic data under undisturbed conditions over one year, the study demonstrates an operational protocol to identify occupancy scenarios that harmonize public accessibility with safety requirements, by experimental assessment of the human impact on inner environment. The proposed protocol is designed to be adaptable and replicable for similar cases, supporting decision-makers in scheduling and managing touristic exploitation, depending on specific visit schemes and modalities.