Ever since Alexander Thom visited Calanais in the Outer Hebrides, groups of Neolithic monuments in western Scotland have been studied in relation to the land and the sky. Less attention has been paid to their close relationship with the sea. These places were secluded and could be difficult or dangerous to reach, yet details of their architecture suggest that there were close links between them. How important were long distance connections between 3000 and 2000 bc? Were some ceremonial centres visited by boat? And was the journey itself treated as a rite of passage? The case extends to structures in Orkney and Ireland.