Watched a programme on Stonehenge the other night, with archaeologists in good standing on it. It turns out that at about midwinter, there were huge gatherings in Durrington Walls, at which people feasted on pigs which were about nine months old. Strontium testing of the pigs' teeth showed that they had been brought to Stonehenge from all across Britain, some from as far north as Sutherland. (I thought you couldn't drive pigs, but the evidence is convincing.) Not from Orkney, though, despite recent connections being found.
There is a route from there to the Avon, on the line of the midwinter sunrise, and it was suggested that the people travelled on the river to the avenue to Stonehenge on the line of the sunset.
The bones from the Aubrey holes, now believed to be the first location of the bluestones, come, like the stones, from the Prescelli area. An extraordinary journey to go to bury people.