M-W
Main Entry:
retired
Function:
adjective
Date: 1590
1 : secluded <a retired village>
2 : withdrawn from one's position or occupation
A retired nook is a secluded corner of somewhere. It's possible that people could retire to the nook, but I doubt whether that's the primary meaning, and a retired nook does not have to admit people. (My cat has several retired nooks that I wouldn't fit into).
One could describe a 'hidden cave' as a cave that people could hide in. But that's not a definition. It's only hidden because it's hidden from people, and hence if people are in it, they are hidden from other people too. It might not be a hidden cave to bats, and therefore bats could not hide in it from other bats.