This is a really varied trail route. It covers sweet singletrack descents through forest descents, open countryside farm land that goes on for miles and a few decent steep challenging climbs to keep the heart rate up.
It is a tough route not because it is so technically demanding but more because of it's distance (It is 50k with 820 metres of climbing!) and it has some fun ambiguity in track direction. Good map reading or a handy GPS would be recommended. I closed the route at 54k being I went in the wrong direction for 2k and then tracked 2k back...but luckily just the once. Although the detour was a great track in itself;)
I used the MRB route card as my initial guide (great these things to map out the route onto a decent sized Ordnance survey map). For me this was the OS Landranger Series (1:50,000) 175 Reading and Windsor as well as a little section of the 165 Aylesbury & Leyton Buzzard.
You can park on the road or in a small turning off the main road just in Nettlebed North of A4130 (OS175/SU70386). Then head down the hill to the main road and take the left to the roundabout. Then straight over for 700 meters and take the bridleway on the right. The route from here is a great taste of what is coming. Lovely little descent down. Go through the woods and at the bottom bear to your right then left onto a track. Turn right to go uphill at the first fork and then bear left at a X roads when you enter the woods. Turn left at a junction by the Estate office. I remember seeing a few similar options so good to check on compass here. Follow this track back into the woods. Continue until you get to the road.. turn right and continue down to the B491 where you turn left.