Where to start??? That's a blank canvas and a half
Some will depend on where you are staying as getting to places like Wasdale or Ennerdale can be very time consuming!
But many walks spring to mind - how about a circuit of the Coniston Fells - Walna Scar Road, Brown Pike, Dow Crag, The Old Man and then down (you can extend this if feeling good, by taking in any or all of the other fells, such as Brim Fell, Swirl How, Wetherlam).
Newlands Horseshoe, Coledale Horeshoe - which you can shorten and lengthen as there are plenty of escape paths. In fact any of the classic horseshoes!
If it was me and I had to base myself in one place, I think it would be Wasdale - a day on Great Gable/Kirk Fell, one on Scafell and then one on Yewbarow, Red Pike, Scoat Fell, Steeple etc. Stay at the Wasdale Head, no need to use the car - bliss. Having said that, if you ask the same question tomorrow I'd probably think of somewhere else!