Depending on where you stay and how long you are there have a drive east through Thirsk and the the Vale of York. Treat the g/f to a top notch lunch at the Star Inn at Harome - very close to Helmsley, which also would be a lovely place to stay, although not in the Dales, and very close to Castle Howard.
Otherwise another vote for Wensleydale, or Grassington in Wharfedale is a lovely central spot for exploring the Dales with some lovely walks. Richmond with its castle is worth visiting, Masham with its two breweries is also worth a stop, and a visit to Fountains Abbey and Studley Royal is also recommended.
Basically you can't go wrong wherever you stay or go!
An exiled Yorkshireman