This article presents an interdisciplinary study carried out on two Recent/Final Neolithic gallery graves (Kernic and Lerret) located on the northwestern coast of Brittany (western France). These monuments show striking similarities in terms of architectural style and geographical position. This paper aims to provide a better understanding of the construction strategy of these monuments by : (i) determining the origin of the megalithic blocks from petro-structural analyses, (ii) reconstructing the coastal environments from the analysis of sediment cores, and (iii) defining the place of these monuments in the territories from intervisibility analysis. The study reveals important differences between the two monuments. The Lerret gallery grave was erected in direct proximity to a unique source of rock material on the margins of a marshland zone. In contrast, the Kernic monument shows a deliberate diversification of stone extraction sites and was established on the edge of an estuary. An intervisibility analysis shows a dense network of visual interconnections between the megalithic tombs in the study area, in which the two monuments occupy very different sites. The social dimensions of stone selection and the geographical location of Recent/Final Neolithic funerary monuments are also discussed in an enlarged regional context.