Looked at on a map, NCN 66 takes an eccentric course across Northern England - one minute heading south, the next taking an abrupt turn north. That aside, this route is developing into a magnificent tour of the central Pennines.
The core is the, sometimes very scenic, Rochdale Canal and Calder & Hebble Navigation; the Spen Valley Greenway railway path from Dewsbury to Bradford; and the Leeds & Liverpool Canal on into Leeds itself. Cycling through such a built-up area on traffic-free green paths is a rare privilege, and one to be savoured.
Further paths and minor streets connect these together, but note that the route isn't quite finished; in particular, there's a missing section around Brighouse which Sustrans are working on right now.
After Leeds, it's minor roads and occasional paths through York to the market towns of Pocklington and Market Weighton.