This is the 373rd most frequent Polish word.
regionu
The Polish word "regionu" means "of the region" in English.
Here, 'regionu' is in the genitive case as it indicates possession in association with 'kultura' (culture).
Kultura tego regionu jest bardzo bogata.
The culture of this region is very rich.
In this sentence, 'regionu' is not directly present but its plural form 'regionach' is used in the locative case, indicating the locations traveled through.
Podróżowałem po kilku regionach kraju.
I traveled across several regions of the country.
Here, 'regionu' is in the genitive case to express 'of each region' in the context of the object affected by climate change.