The remains of the Horslip long barrow can be seen from the track leading up from Avebury Trusloe to Windmill Hill, although there's not much left to see. It has been ploughed out and is now just a barely discernible mound in an arable field within 100yards of the bridleway.
As far as we know, the Horslip long barrow is the oldest monument within the Avebury World Heritage Site. It was partly excavated in 1959, from which a date range of 4240-3810 cal BC was recorded.