I visited Stonehenge this past May. The sky was gray and it was drizzling. Unfortunately I was on a bus tour and because it was a Saturday, there were many other people there as well, so I really wasn't able to pick up any feelings about the place. But I do know what you mean about a "foreboding experience" and feeling of "dread" about a place. My first visit to Andersonville Prison (Civil War POW) in Georgia made me feel that way. I was practically alone walking around the grounds. I couldn't shake the feeling of sadness that had come over me. It wasn't until I had left the place and was on the road that I started feeling better.
Unfortunately, there are too many risks these days to allow people to get that close anymore. It was one of the great thrills of my young life to sit on those stones, where, perhaps, some of my ancestors visited.