Well done, BuzyG.
Not done anything crazy for a while, but I recall 4 particularly tough outings:
37 miles along canal towpaths whilst I was a student in Birmingham.
A solo 26 mile trip traversing above the western flank of the Valsavarenche valley on the last day of a 2 week trip to the Italian Alps. Magnificent walking just below the snowline about 8000' up, but lots of ups and downs. And I made the mistake of wearing shorts, so the back of my calves got frazzled in the Alpine sun.
The Welsh 3's. Similar distance, more ascent, less sun! A brilliant walk, but not one that I will repeat.
Finally, a non-walking one - the Bealach na Ba cyclosportif - 90 miles of up and down; nearly killed me, but I did finish. 550 starters - I was 7th from last - but 70 didn't make it to the end. Made it onto the telly too - they obviously needed a victim at the end of their tether to film!