Route: Pennine Way (UK)
"Steeped in history, this National Trail chases along the mountain tops along the rugged backbone of England and offers 268 miles of the finest upland walking in England. A once in a lifetime experience."
The Montane Spine Race covers the entire Pennine Way in winter. The overall course record was set in January 2019 by fell running phenom & nursing mother Jasmine Paris in 83h12m23s: https://www.bbc.com/news/uk-scotland-edinburgh-east-fife-46906365