Joshua Slocum solo sailing around the world in the 1890’s. The man certainly knew something about being alone! Oh, and cannibals.
Beyond that, definitely agree with he Caird journey. I’ve been cold, bitterly cold, lost feeling in my feet and having trouble getting my hands to work. But I can’t for the life of me fathom the misery of that journey. Particularly near the end where it is likely that if Shackleton had succumbed to sleep he would not have woken and the record of that journey would have been quite different.