Given that the structure is visible from so many viewpoints, how easy (or difficult) would it have been to work out the right spot to build it (assuming its position was worked out and the ‘multiple viewpoint effect’ didn’t just happen by accident). It can be seen from as far away (the furthest point?) as Winterbourne Bassett, from within the Avebury circle and from so many other vantage points both near and far. That really is an extraordinary achievement when you think about it.