Location, location, location
I'm based approximately at the point where the A22 and A23 meet in South London. Just on the edge of the North Downs, places like Leith Hill are about 30 minutes away by car, a bit longer by train or riding.
Most of the time I am up and down the A23 to the City "like the Asyrian Empire".
I have been on a couple of "Tour de Cake" rides and a couple of proper rides. The proper rides were quite hard work, but worth the effort.
On occasion I will jump on the bike and go exploring the off road potential of the local area. Recently; Oxleas Wood (Eltham) and Mitcham Common (Croydon) have been a couple of pleasant surprises. Next on my radar are the Shirley Hills, there are no official mtb routes, but I have been recommended to go explore.