They are trying to restore the lanscape to it's original form and the proposal is for the visitor centre to look like a stone wall so that it doesn't impinge on the vista (I bet the architect gets a nice fat fee for that idea). Why not hide it completely by building it into the reverse side of a small hill? Come to think of it, maybe "re-excavating reprofiling the tunnels" is a euphemism for turning Silbury Hill into the visitor centre. ;o)

Steve