Whizzing by

As part of the continued celebrations of mother's 60th birthday (she's a lucky devil, it's been going on for months now!) we decided to take the old dear away for a surprise trip ... more on that in the next blip, this was snapped as we rushed past Stonehenge (pa slowed down so I could snap this quickly). I've been past the spot a few times but it never fails to awe, and to confuse...what IS it there for? And why does it still hold such a sway over us?