Situated about a mile north of Stenness, along the road towards Skara Brae, is this wide circle of standing stones, some over 5m tall. Last of the three Stenness monuments to be built (2500–2000 BC), it remains a most atmospheric location. Twenty-one of the original 60 stones still stand among the heather. These mysterious giants, their curious shapes mutilated by years of climatic onslaught, fire the imagination – what were they for? On a grey day with dark clouds thudding low across the sky, the stones look secretive and seem to be almost sneering at the jostling summer crowds. Free guided tours leave from the carpark at 1pm from June to August.