Ouch, nice one MatthewJDB thanks for that!
I especially like the fact he puts Nate's post at the beginning.

If I don't watch it I can still pretend it can't be done, right?

*Reads the first post of the topic*

I just saw some pilled rocks around it and climbed like if they were stairs.

Kinda reminds me at point of the game, I saw a chest on a corner of a roof of a wooden house, but I couldn't reach it. If I'm not in error it was when I was looking after Packrat Palooka or the next outlaw, I'm not sure. There was a rope close but it was too far to give a leap until there.

I managed to get the 40 chests achievements even by skipping that one.