Windmill Hill is a Neolithic causewayed enclosure on a rounded chalk hill about two kilometres northwest of Avebury, one of the earliest known examples in Britain. Dating from around 3700 BC, it predates the stone circle by roughly a thousand years, and was used as a gathering place — archaeological evidence suggests feasting, exchange of goods, and possibly burial rites, though not as a permanent settlement.
The hill itself is reached by footpath from Avebury and offers fine views over the surrounding downland. The earthworks — three concentric interrupted ditches — are low and unspectacular compared to the stone circle, but the site's age makes it a remarkable footnote in the Avebury complex. English Heritage manages the site and it is freely accessible.