Upon further investigations the London Walks group has special visits to Salisbury (including Cathedral) and Stonehenge for the solstice and equinox occasions. They are a group of professionals who walk you for 2 hours around London and stop at pre-determined places to tell you about the architecture, noteworthy people, history and stories of the city. Quite delightful and addictive. We joined their tour and had a fantastic day.
There are many theories why Stonehenge exists, one of many arranged groups of over-sized rocks around the UK. What makes these various stone piles interesting? The stone is not often not native to the area (Bluestones, Sarsens), they are gigantic and heavy, and organized in an intricate pattern. One can deduce that they have therefore been moved to this location by people, who used technology for movement, and arranged them according to their needs. By whom? How? For what? These are unanswered and highly speculative questions with no decisive answers.