Tempted to do the pennine bridleway as a bivi trip this year myself. Waiting till the warmer months kick in and then will just go for it one fine weekend. Would do south to north and get as far as top of Mary Townley then bike on to Keighley and then canal back to Leeds.
Other one I wanted to do was work out a Carlisle to Leeds route similar idea to The Dales Way walk then catch a train and bike back.
These are just two, I have loads and loads of ideas. Basically get a map and have a play.
Basic ideas usually consist of going a long way away and then biking back.