One of the largest Neolithic chambered tombs in Britain, West Kennet Long Barrow was built around 3400 BC. You can explore all around the site and also enter the tomb, which was used for more than 1,000 years before the main passage was blocked and the entrance closed, around 2000 BC. More than 300 feet long, it has an elevated position with a great view of Silbury Hill and the surrounding countryside. It's about 1 mile east of Avebury.
Avebury, SN8 1QF, England