In reply to echo34:
I did the Pennine Barrier 50 miler a couple of years ago and would highly recommend.
It starts at Malham, goes up the cove, past the tarn and over Fountains Fell, then does the Yorkshire 3 Peaks loop before returning the same way to Malham.
For me it was that sweet spot of hilly enough for a bit of variety and good views/mental checkpoints, but not so hilly that you're basically on a long walk. Great views of the Dales, nice running terrain, well organised and supported.
When I did it, I think it was June but looks like next year's one is in May:
https://www.gbultras.com/pennine-barrier-50/