Stonehenge is a World Heritage site, acknowledging the uniqueness of this remarkable feat of prehistoric megalithic engineering.
The Heel Stone is an outlier - a standing stone outside the main circle, often used to set an alignment. Common knowledge has it that the midsummer sun rises above the Heel stone at Stonehenge, which is not strictly correct. Recent archaeological work has discovered that there was another stone next to the Heel stone. It would have been along the fence and towards you a bit in this photo. The alignment was between the two outlying stones.