Dylewo (German: Döhlau) is a small village located in the Warmian–Masurian Voivodeship near Ostróda. It was at the turn of the 19th and 20th century that the then owner, collector and patron Franz Rose, expanded the estate, transforming it into a model example of a manor–park complex on the lands of former East Prussia. Especially the manor park, with its refined composition, valuable tree stands, original architecture, and high–class sculptures, is recognized as an outstanding artistic achievement. Today, it is difficult to spy this former glory amidst the village structures—a neglected park that has grown wild and buildings progressively demolished or falling into ruin. To date, no comprehensive study documenting the overall look of the complex has materialized. This article contains an introduction to a scientific–research project as well as a summing up of the first phase of work—an inventory survey and examination of the history of the Exaltation of the Holy Cross filial church in Dylewo. The text presents measurement documentation performed within the framework of an August 2023 study trip as well as the results of in situ research conducted on the architectural transformation of the church. Using accumulated archival materials, field research, and comparative analyses of churches in the region as a base, the history of the church was retraced and successive phases in its building were recreated. Special attention was applied to the use of remnants of older structures within the existing building. Attention was also called to the fate of selected works of art making up a part of its original furnishings that were later kept on the grounds of the church—the sculptures by Adolfo Wildt. Also analyzed was a hypothesis that assumes that the architecture, décor, finish, and furnishings of the church may contain motifs of symbolic nature making up a part of the ideological program accompanying the composition of the whole of the manor–park complex. The performed measurements and research confirmed the history of the church as recreated on the basis of sources, while preserved fragments of Medieval walls proved the many centuries of continuity of existence of this sacred structure on this site. The church has turned out to be a significant component of the manor–park design maintaining it in a symbolic style. In light of the involvement of several leading artists of the time, including garden designer Johann Larass, painter Josef Huber–Feldkirch, and sculptor Adolfo Wildt, the conducted research seems to go decisively beyond the local context and is original input into the understanding of the European culture and art of this period.