Follow Baza's directions. I found the private road as directed by Baza easy enough. TIP - when walking up the private road keep to the right of the road. The burial chambers are NOT visable from the road. About 30/40 yards up the private road (from athe main road) hop over the fence on your right (be careful - fence is barbed and the side of hill is steep). Carefully move about 5 yards down side of hill and you should spot the chambers to your left - sunk into the side of the hill. Only the front part of stones showing. Hope this helps?
Coming to Avening from the site of Oldfield Wood long barrow (21.3.2009) - I failed miserably to find the chambers along the side-road mentioned by Baza. I wandered round for a while, but gave up as time was getting on - Avening is a nice village, with an unexpectedly lovely Norman church and a couple of nice-looking pubs. But I had to press on to Norn's Tump, so I'll have to come back another time to find the chambers.
The chambers are still there and I just visited tham. 2 are roofed and one you can get inside. Not easly to find but persistence pays. It's great they have survived their travels.
DrMike
I visited Avening in Sept 2003 in an attempt to find these burial chambers. After trespassing all over the site someone appeared and asked me what I was up to. On being told of my quest, they informed me that there's been a lot of changes in the area and the burial chambers have gone.
Update:
I revisited this site on 30/5/04 and, I'm pleased to report, the burial chambers are still there, although they are very neglected and appear to be disappearing back into the earth, with only the tops of the chambers still visible.
This time, instead of approaching the site from the village, I parked my car in Avening and walked north along the B4014 until I came to a private, unmetalled road going south-east up a hillside. Within 100 yards I could see the chambers, behind barbed wire and set within a steep bank on the right-hand side of the track.
I found an account at http://www.stonehenge-avebury.net/tourglos.html
of a Megalithic Society tour of South Gloucestershire in 2000, and although they didn't actually visit the chambers, the way the piece is written suggests that someone had visited them in the recent past.
It says: "They are built into the steep hillside of the garden of a house in Lower Avening (at ST 879983), but visits are best left for winter. Permission to inspect is readily obtained." [by the look of the map though, there aren't any houses at this grid reference]
I'm not saying baza's informant was lying. But you know how people frequently don't know what's on their own doorsteps. I just want to hold out some hope they're still there somewhere.
These three burial chambers were (for some reason) moved to this site in 1806 after the excavation of a long barrow south east of the nearby hamlet of Nag's Head.
Two of them are roofed with single capstones and have short passages as approaches. They are particularly interesting because chamber 'III' has an artificially cut porthole entrance - probably for popping your ancestors' bones in and out with - and chamber 'II' has part of what might be one: it has semi-circular notches at the entrance.
(info from James Dyer's 'Discovering Regional Archaeology: The Cotswolds and the Upper Thames' 1970 - I trust the chambers are still there.)
Following the revelation that they are not :(
I tracked down some more information at a transcription of George Witts's Archaeological Handbook of Gloucestershire (c1880) (see link in the general Cotswolds section). He says that the chambers were moved to a 'grove in the rectory garden' - does this shed any light? Or is that where you were looking, baza? If they've just been lost altogether and aren't in any museum that would be ridiculous considering the apparent rarity of them with their portholes.