Possessive nouns

[dolcecasa]

Hello,
One of my Italian students recently wrote "they entered the library of the monastery" in a book review. I corrected her with "they entered the monastery's library". Now I am doubting my correction. What are the rules for common nouns and possession?
Obviously grammar is not my strong point. Looking forward to some help.
Ciao

[Jo]

Probably the most natural way to say this is "they entered the monastery library", as in "hotel restaurant" and "car door".

However, in certain circumstances "they entered the monastery's library" could be appropriate - for example where you want to emphasize the monastery or its importance, relevance to the situation etc.

"They entered the library of the monastery" is not really idiomatic, though it is not wrong grammatically.