In one day - Lyke Wake Walk (a few times), The Shepherd’s Round (devised as an alternative to the LWW when it became too popular (hah!!) - very tough, starting and ending in Osmotherley), both approx 40 miles. The Hambleton Hobble, same principle as above, but shorter - approx 30+ miles. Byrness to Kirk Yetholm - the last section of the Pennine Way - 25 very tough miles. Yorkshire 3 peaks, ditto.
I used to lead a walking group in the area every match weekend - usually, Sundays, obviously - I devised loads of different routes and we averaged about 15-18 miles each time, but a couple in the 25 mile range.
In one ‘go’ - Pennine Way 268 miles, Coast to Coast (lots of times) 193 miles, West Highland Way 96 miles, Cleveland Way 109 miles, Wainwright Whitsun Walk 107 miles and 40,597 feet of climbing - far and away the hardest!!!
I also climbed all 214 of the Wainwrights in one year about 12 years ago.
I do much less now, having got that lot out of my system, and haven’t walked more than about 15 miles in the last 10 years. As I'm 66 now, that doesn't seem unreasonable!