For they were looking down into a shallow depression in the valley, like a sort of natural crater, brilliantly lit by a light source that Hermione couldn't detect. It was a perfect circle of lush green lawn untouched by the weathering all around it. At the centre of it was a dome-shaped earthwork mound, and atop that a row of three concentric rings of perfectly carved oblong standing stones, all crowned by heavy lintels. The monument was silvery blue in colour and each stone shone as though producing its own light. The whole place thrummed with a low vibration of energy that Hermione could feel resonating in her bones.