This study investigates the ecological symbiosis between traditional rural buildings and wildlife, using the European hornet (Vespa crabro) as a representative case. Located in Toutosa, a village in Northern Portugal, the research explores how vernacular architectural features—such as unused chimneys built with natural materials—can inadvertently provide suitable nesting habitats. Technical characteristics of a European hornet nest discovered in a chimney were analysed, alongside architectural and environmental data. The paper discusses both the opportunities and risks associated with wildlife cohabitation in traditional buildings and reflects on broader implications for biodiversity-sensitive rehabilitation. Although preliminary in scope, the study offers insight into how traditional construction practices can support wildlife under certain conditions, suggesting potential applications in sustainable and biophilic architectural design.