I've been a few places gang wars were prevalent.
I've been a few places gang wars were prevalent in.
I've been a few places where gang wars were prevlant.
I've seen people use place(s) both with and without a preposition, still the first example sounds a tad weird, which is why I post this question. Is the first sentence grammatically correct? If so, can we drop these prepositions anytime we want, or does it always depend on the context?