Proud to say I accomplished that! My dad trained a fair bit. I did like 1 10km walk the week before we started, and I finished the 800kms with no real dramas, except the first day which was a massive climb. After 5-6 days my body was totally accustomed to the task at hand.
(Super irrelevant to the post but it was an awesome experience and I would advocate anyone to undertake it, regardless of your thoughts on religion. I am not religious but did find it spiritual in a way. I did it about 6 years ago and still think about it every week.)
Seeing the public reaction to some of the military adjacent cases over the past few years has been incredibly disheartening (e.g. McBride)