There is a reasonable loop that starts in Ticknall, through Robin Wood, Repton Shrubs, Foremark Reservoir, 50% offroad, about 15 miles in total + 6 miles each way to Lount – it'll be a bit of a quaqmire in places, but at least it's "mountain biking", I'm sure someone else'll chip in with more details before the weekend, but if they don't I'll return with more detail.