Unfortunately the stones, for their own protection, are roped off. You can walk around them, but you cannot touch them.
In 2013 English Heritage opened their new visitor center at the site. We went to visit the stones, and to see the new center, on a very cold and wet afternoon in January 2014. We have never walked around those stones so quickly in our life as we did that afternoon! We were certainly glad to get back into the warmth of the visitors center, to which we discovered we were the only idiots who would venture out in such awful weather - we had the center practically to ourselves. Inside the center they have this marvelously roundish room. We sat down on the floor, in the middle of this room, and watched the virtual tour of Stonehenge. The tour takes you from the beginning of the monuments history, until modern day. It was very impressive and helped us appreciate just how old these stone are.
I am not surprised that Merlin found his way to Stonehenge. I find it hard to conceive just how our ancient ancestors moved these stones. Maybe, along the way, there was a little magic to it. I like to think so anyway.
Geoffrey of Monmouth The History of the Kings of Britain.