Firstly - thanks for all these suggestions! Having had a bit of time to explore the area myself too now, I thought I'd add in a couple of extras that I've found/being shown.
TURVILLE - just North of Henley. Little village that is purportedly amongst the most photographed and filmed in the UK. Midsomer Murders, Vicar of Dibley, Jonathan Creek - type places. Plus of course COBSTONE MILL (in Ibstone) just on the hill and Caractacus Potts' workshop in Chitty Chitty Bang Bang....if you like that kind of thing....
Nearby there, just to the West, I've actually also been shown a rather interesting tree layout that looks notoriously like a swastika! Somewhere down the Thames Valley between Stokenchurch and Henley. I think around the - unfortunately named - Pishill. Found it once, never found it again. The story I've been told is that it was on the site of an old WWII POW camp (Camp 246 - North Camp, Nettlebed as you ask...) and that the German prisoners surreptitiously planted the trees as part of their work for the Forestry Commission. Only years later were they visible as the Nazi symbol. I'd dismiss that as folklore if I hadn't a) seen it myself and concur....it is very much like a swastika ... minus one of the hooks nowadays and b) there is a nearby Union Jack on the ground quite visible as something of a retort....
Going a bit (ok, a lot) further north-west is a spot just within the Kemble ATZ, south of Coates. Allegedly the source of the Thames. Now THAT would be a navigation exercise for a PPL student.... (51.6986575,-2.0426561 as far as I can ascertain....happy to be corrected on that)
And finally, north of Sydmonton (a few miles West of Kingsclere Mast) is Andrew Lloyd Webber's house, complete with own personal church in his grounds! 51.3180041,-1.3063539 if anyone wants a closer look.