More information: http://en.wikipedia.org/wiki/Blowing_Stone
The Blowing Stone is a perforated sarsen stone in a garden at the foot of Blowingstone Hill just south of the Icknield Way (B4507), at Kingston Lisle, near Uffington. The stone is capable of producing a booming sound, when anyone with the required skill blows into one of the perforations in a particular way. . Also, according to legend, a person who is capable of making the blowing stone sound a note which is audible atop Uffington White Horse Hill (where Victorian antiquarians thought King Alfred's troops had camped) will be a future King of England.