This is the 8475th most frequent Russian word.
неизвестно
"Unknown" or "uncertain."
In this sentence, "неизвестно" is used as an impersonal word indicating lack of knowledge about the subject (who came to visit).
Неизвестно, кто пришёл в гости.
It is unknown who came to visit.
Here, "неизвестен" is the predicate and emphasizes that the movie is not known among the general audience.
Этот фильм неизвестен широкой публике.
This movie is unknown to the general public.
In this context, "неизвестную сторону" uses the adjective form "неизвестную" to describe the direction as not known or unrecognized.