Thats called the Hunter's Lodge (maybe) henge, there's a bit of confusion because of the mound in the centre; either B/A disc barrow or a neolithic henge.. It has an internal and external ditch on either side of the bank, plus pits, and maybe the bank was a series of pits, its complex, could be multi period. All that taken from Jodie Lewis - did no one else in Somerset fork out the £35 ;) it also has confusingly another smaller inner ditched enclosure, probably for keeping the pigs in..