This is the 10827th most frequent Polish word.
dzielnicach
"Districts" or "neighborhoods" (locative case, plural form).
Here, 'dzielnicach' is the plural locative form of 'dzielnica,' indicating places where the action of living takes place (in districts).
Mieszkam w dzielnicach Warszawy pełnych zieleni.
I live in the districts of Warsaw full of greenery.
In this sentence, 'dzielnicach' refers to 'districts' in a locative case, specifying where cultural events occur.
W tych dzielnicach kulturalne wydarzenia są bardzo popularne.
In these districts, cultural events are very popular.
Here, 'dzielnicach' is used to specify the areas being traveled through, employing the locative case to show location.