Looming 30 meters (98 feet) over the Avebury countryside, the steep grassy slopes of Silbury Hill are an incongruous sight against the backdrop of gently rolling farmlands.

This is no ordinary hill, however - the fascinating man-made structure dates back to around 2400BC and is the largest prehistoric monument of its kind in Europe.

Experts have long debated the significance of Silbury Hill, but while there are few indications of its actual purpose, its size (comparable to the Egyptian pyramids) and careful construction are none-the-less impressive.

The mysterious hill also makes an intriguing addition to England's UNESCO-listed Neolithic monuments, which include the Avebury Ring, the West Kennet Long Barrow and Stonehenge.