Avebury is predominantly a wideangle lens location, perhaps close-in with the stones towering over you, using long exposures to allow the clouds to blur through the shot. My go-to lens is the Nikon 24-70mm.
A selection of filters is handy: a polariser for eliminating haze, brightening blue skies and adding contrast, and a Lee Filters Big or Super Stopper to achieve long exposures to blur movement in the clouds.
It goes without saying that a tripod is vital when using filters to shoot long exposures and when shooting in low-light conditions. Fortunately you don’t have far to walk so you won’t need to lug it around for too long.