Bulmer/Castle Howard run. Virtual Earth route map.
(When in Virtual Earth click on hybrid view to get a satellite image overlaid with the map, use the zoom function and download the 3D installer ((it's free)) to get a better idea of topography and elevation changes.)

   Over the years many club members have enjoyed training runs in the splendid Howardian Hills around Castle Howard. This used to be a regular Sunday morning fixture and the 13/14 mile route is excellent marathon preparation.
I have added a map  which has a suggested route (and two alternate routes)  beginning at the village of Bulmer, recently a tea shop has opened in Welburn so you could start there (pushpin 4) if you fancy some post run refreshment.
You are advised to cross check the online map with a proper Ordinance Survey map, be physically capable of running for 2-3+ hours and to have the correct attire for off-road running.

Bishop Wilton 15 mile trail run. Virtual Earth route map.
(When in Virtual Earth click on hybrid view to get a satellite image overlaid with the map, use the zoom function and download the 3D installer ((it's free)) to get a better idea of topography and elevation changes.)
 
Another favourite training run begins at the village of Bishop Wilton.
Plenty of hills and a distance of 15 miles make this a bit gruelling for the un-initiated, but the splendid views over the Vale of York go some way to make up for the effort expended.
You are advised to cross check the online map with a proper Ordinance Survey map, be physically capable of running for 3+ hours and to have the correct attire for off-road running.

Various mapmyrun.com routes in York area:

1.City centre / River / Fulford Golf course / Hull Road (13 miles).