I'm rather looking forward to it :-)
2.5m across !!! http://web.jet.es/jose_barral/petrotel/wgr2004/wgr2004_f05.htm
Apparently there's one near this with 18 concentric circles that's 4m across. Yikes!
I thought it was 17 ,but if it is 18 then that makes it more interesting numerically because there is nothing close in the UK and Irleand but there are quite a few with 9 rings .