Come to the crest of a hill at the very heart of Scotland where you can see islands off the west and east coasts of the country, to a place that was sacred for over 4,000 years. Try to decode the mysteries of how neolithic material was re-used by later people at this very complicated site and pick a side in the long-running debate: was the circle here timber or stone?

Guest: National Museums Scotland research fellow Alison Sheridan.