The A666 is a major road in Greater Manchester and Lancashire, England. Known as 'Bolton Road', or 'Blackburn Road' depending on which area it is in, it runs from Pendlebury near Manchester, through Bolton, Darwen and Blackburn before meeting the A59 at Langho. Along the route are the West Pennine Moors, the Turton and Entwistle reservoir and the Entwistle reservoir forest.
It is sometimes referred to as "The Devil's Highway or "The Devil Road" due to its 'satanic' numbering, as well as its high accident rate on the moors between Egerton and Darwen. Conversely, for a short length in central Bolton, it is known as "St Peters Way"