Visited Stonehenge on a very cold and windy day in early February 2012. We (regular tourists) were not permitted to enter the stone enclosure itself and had to keep on a paved pathway some distance from the monoliths as we circumnavigated the site.
At the time of my visit, the parking lot, admissions office, gift store, restrooms, etc. were on the far side of the very busy main east-west road. All very low key facilities. You reached the archaeological site on the other side via a pedestrian tunnel. Recent news articles report that the main road that ran close to the site is being/has been rerouted to restore the open plains setting of the historical site. Hopefully, they’ve also improved the facilities.
My understanding is that the hippies you are worried about only really visit the site on the key days of the astronomical calendar (equinoxes, etc.)which have significance in their Druid/occult practices. If you attend one of their events, you would be allowed to enter the stone circle and do all manner of things that an actual tourist would probably be fined or arrested for.
I attended a few “pagan Druid” circles in Venice Beach. They are seriously no more impressive than your average Star Wars convention or Renaissance Fair.