This article presents an interdisciplinary study of two Late/Final Neolithic gallery graves (Kernic and Lerret) located on the orthwestern 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 using comparative petro-structural analyses of blocks and surrounding rocks, (ii) reconstructing the coastal environment 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 studied. The Lerret gallery grave was erected close to a unique source of stone material on the margins of a marshland zone. In contrast, the Kernic monument, erected on the edge of an estuary, seems to have been built using a deliberate diversification of stone extraction sites. 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 implications of stone selection and the geographical location of Late/Final Neolithic funerary monuments are also discussed in an enlarged regional context.