Geograph - photograph every grid square

The village of Avebury is home to one of the most complex and extensive Neolithic (late Stone Age) sites in the whole of Europe. It is a henge monument meaning it comprises a circular bank with an internal ditch. Its circumference of over 1000 yds/metres makes it by far the largest known example anywhere from this date (c.4000 BC).
Within the henge is the great outer circle - the largest Stone Circle in Britain and one of the largest in Europe.
Within the large circle are two smaller circles, the central inner circle, with "The Cove" at its centre, and the southern inner circle which has "The Obelisk" at its centre.
There is thought to have been a northern small circle too, which partly crossed the northern perimeter of the main circle, but little of this remains.
To the south of the great circle runs the Kennet Avenue of stones, this double row of stones c.30yds/25m wide runs for about 1½ miles (2.5km) in a straight line from Avebury to "The Sanctuary"
The area around Avebury is dotted with numerous Stone Age features, such as Silbury Hill and West Kennet Long Barrow; The Sanctuary and Windmill Hill.
Not far away is the famous Stonehenge and together these ancient sites form a UNESCO World Heritage Site Link

Much of the Avebury site owes its present good condition to the work of Alexander Keiller Link who spent most of his own personal fortune excavating and restoring the site in the 1920s. Many of the stones had been buried and he re-erected them and saved many artefacts that now form the basis of the museum in the village. In 1943 Keiller sold the estate to the National Trust for just £12,000 being the agricultural value of the land.
Many of the ancient stones have disappeared - perhaps a few may be discovered in the future. At present, missing stones are marked by small concrete obelisks which Keiller originally installed.

Not surprisingly, the whole site is a Scheduled Ancient Monument - see EH listing here Link
It also has a World Heritage Site listing with EH Link (see also link to UNESCO above)