Having georeferenced the official plan of the new Stonehenge Visitor Centre in QGIS (as discussed in an earlier post) I was able to determine the coordinates for the end points of the "Avenue" through the middle of it.
Armed with my GPS, I then went out to the location and planted sticks in the ground at those end points, then walked back to the previously determined observation point and took a few photos to assemble into a panorama.
Finally, I scaled and overlaid the west elevation of the architect's drawings for the new building on that panorama to get a (rough) idea of what it'll look like.
Sunrise on April and September 6th (or thereabouts) each year will be on this alignment, and the Sun will appear to rise out of the ticket booth :-/
I stress again, this is pretty rough and ready, but it's just to give me (primarily) an idea of how it may look.
(Apologies for the wide page the panorama requires to be viewed)