This is the 1849th most frequent Polish word.
gdynia
Gdynia: A city in northern Poland, located on the Baltic Sea.
In this sentence, "Gdyni" is used in the locative case, indicating the location where the action takes place.
Moja babcia mieszka w Gdyni.
My grandmother lives in Gdynia.
Here, "Gdyni" takes the genitive case, commonly used after prepositions indicating movement towards a direction, such as "do" (to).
Jechałem do Gdyni w zeszły weekend.
I traveled to Gdynia last weekend.
In this sentence, "Gdynia" is in the nominative case as the subject of the sentence, identifying the city being described.