Why Was Stonehenge Built?

The AskHistorians subreddit on what the best accepted explanation for Stonehenge is:

They believe that Stonehenge is a domain of the dead; there are no signs of habitation there, there have been many high-status graves found, they suspect that the stone material is associated with death, and that the significant time of year for the site is the Winter Solstice. Conversely, nearby Woodhenge is a domain for the living; there are many artifacts pointing to large-scale winter feasting, evidence of a nearby settlement, and they believe that the wood material is associated with life. Both Woodhenge and Stonehenge are connected to the River Avon by their own "avenues", i.e. causeways running between the sites and the river. Further, the Stonehenge Avenue runs atop a natural fault/formation which is aligned with the Solstice (which they speculate may be the reason Stonehenge is located where it is). So, they imagine that there may have been some kind of mid-winter festival at Woodhenge that involved a procession via the river to Stonehenge, where the society would honour their dead in some way.

Also there have been attempts to figure out how the henge was assembled that have had some success: