Creating a conservation project for culturally significant buildings is a complex process that requires good and thorough documentation. The documentation covers various data types that require analysis to solve different heritage problems and obtain accurate data for restoration works. In the case of the St. Basil of Ostrog church in Nikšić, Montenegro, a geometric digital twin (gDT) was created using laser scanning and photogrammetry to provide geometry accuracy and descriptive data of the building fabric. Since its construction, the original architectural drawings from the late 19th century have not been preserved and there is a lack of proper docu-mentation. The Cathedral Church, built in the Byzantine style, is a complex structure consisting of interlinked objects. It has started to show signs of various pathologies that need to be addressed. The photorealistic geo-metric digital twin has been shown as an effective tool for obtaining accurate and descriptive information in the case of intricate heritage buildings. To obtain gDT, different technologies have been used such as laser scanning and areal and close-range photogrammetry. This paper aims to demonstrate how different kinds of digital data (historical, geometric, pathological, and performance) benefit from a geometric digital twin to create a conservation project and continue to monitor this Montenegrin heritage building closely. The conser-vation project of the St. Basil of Ostrog church in Nikšić was created according to the Conservation conditions issued by the Cultural Heritage Protection Administration of Montenegro, which defines what needs to be achieved by the project to improve the condition of the heritage building.