As mentioned by
@DCLane , there is the C2C route. If you wanted something "easier" there is reasonable cycling along the coast, certainly in the direction of South Shields. It is quite possible to make a "loop" of (say) 20 miles, all on tracks, or, quietist roads (we do so regularly hybrids). At South Shields, you could even take the Ferry (or cycle inland a short distance, and use Pedestrian/Cycle Tunnel), and then to Newcastle, or Blyth. There is also cycling along the coast towards Seaham, although, I am not personally familiar with that route.