next time you're in Avebury (which is OK if you like that kind of thing), go up east until you hit the Ridgeway, start walking north, go past Alfred's Camp, go past Uffington, go past that mad place near Wantage where the big heathen rave was, and keep going until you get here:
http://www.themodernantiquarian.com/browse.php?site_id=553

you won't regret it

well, you might, but the exercise will do you good :-)

RG