The article presents the process of structural diagnostics of the Dominican monastery in Lublin. In order to establish the underlying cause of cracks, not only in situ investigations but also detailed analyses of documents were executed. Inventory drawings were examined in order to identify the building’s structural system. The query of historical documents and city archives was carried out to understand the structure’s performance. Conclusions were confronted with the crack pattern. It was established that the damage resulted from the original conditions of the structural system in place. These conditions were created in past, when the monastery incorporated sections of the medieval town wall into its structure. The article details structural remedies applied in the course of rehabilitation. The introduction of supporting structures was the effect of a compromise between the necessity of ensuring structural safety and the demand for the minimum impact on the heritage site. The article aims to highlight that the structural assessment of the heritage asset is an investigative process. The work also emphasizes that in spite of numerous up-to-date methods helpful in the structural diagnostics of building structure, the conceptual analyses of the structural system still remain of vital importance. The query of historical documents helps in determining the structural system of a historic building, and vice versa, structural analyses assist in recognizing and supplementing the knowledge of the asset’s history.