This study presents an interdisciplinary approach of two Late/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 study aims to provide a better understanding of the construction strategy of these monuments by: (i) determining the origin of the megalithic blocks from comparative petro-structural analyses of blocks and surrounding rocks, (ii) reconstructing the coastal environments from sediment core analyses, and (iii) defining the significance of these monuments in the territories from an intervisibility analysis. The study reveals marked differences between the two monuments. The Lerret gallery grave was erected close to a unique source of stone material on the margins of a marshland zone. In contrast, a deliberate diversification of stone extraction sites is argued for the Kernic monument which was furthermore erected on the edge of an estuary. An intervisibility analysis shows a dense network of visual interconnections between a number of megalithic tombs present in the study area, where the two monuments occupy very distinct sites. The social dimensions of stone selection and the geographical location of Late/Final Neolithic funerary monuments are also discussed in an enlarged regional context.