Anyone ever heard of the Duke's Vaunt? It's a very old oak in Savernake forest, possibly 1000 years or so. It is now in serious decline so if you want to take a last look dont leave it too long as there is only one shaky bough left in leaf. Directions can be given but its not easy to find it you dont know the forest well!!
It's at SU237665 but dont go unless you are competent and only try in daylight. Park up on The Grand Avenue opposite the road leading to the Column and Lye Hill, (Three Oak Hill Drive). Good Luck!!
