I did my first ever 100 km audax yesterday from Chalfont St Peter to a cafe on the banks of the Thames at Benson (pictured) , and back via some quite tough hills and narrow country lanes in the Chilterns. It was a good day, and I found the pace about right (13.2 mph average). Some riders went quite a bit faster than me downhill, but my brakes aren't brilliant so I take it steady (I've since adjusted them to make them sharper). The weather stayed dry but was cool. There was quite a range of ages from 20s to 70s and a mixture of bikes from steel to carbon, some with luggage and mudguards - others carrying hardly anything. We spent around 5 hrs cycling - 6hrs in total, and I was glad I didn't do the 200km Anfractuous - which probably meant finishing after dark. Hence the name of the one I did I assume - nyctophobia being fear of the dark.
Map here http://www.bikely.com/maps/bike-path/Nyctophobic-2011