Translation:The town was near but it couldn't be seen.
thanks for stressing this - it had me foxed - have a lingot - DL is great - so very often traditional grammar books aren't overly useful as they don't of course know why you opened the book. Here a puzzled but focused question can, very quickly at times, elicit a focused bit of guidance.
If this is idiomatic Italian, of course I would not argue, but I did not think that "non si vedeva" necessarily implied a lack of ability to see rather than just the act of "not seeing it" i.e. "you didn't see it." So where is the inability to see implied in this construction?
I'm also confused about the "it". To me there is no Italian word for "it" in the sentence - such as "... non lo se vedeva", but to leave it off in the English is not acceptable to Duolingo. Am I right in deducing that, where it is clear what one is speaking about, vedere does not need the "it". Also, does the omission of "it" in the English translation actually make it wrong (rather than just weird), or should I feed that back to Duolingo?
In this construction, it is typically expressing the impersonal "one" person. As in "one can not see it". It is conjugated as third person singular in Italian, and translated as "one" or as "you" in English. As I understand this construction, it is not correct to translate it as "we" because that would be written differently in Italian. (In English, "one" or the ambiguous "you" of recipes and instruction manuals are both impersonal forms, and therefore are valid translations of the Italian "si" form. But "we" is only used in English by royalty and is very presumptuous, so it's rarely used in this way.)