This is the 2481st most frequent Polish word.
grudziądzu
"Grudziądzu" is the locative case of "Grudziądz," meaning "in Grudziądz," a city in Poland.
Here, "Grudziądzu" is the locative case of the noun "Grudziądz", used after the preposition "w" to specify location.
Mieszkam w Grudziądzu od pięciu lat.
I have been living in Grudziądz for five years.
In this instance, "Grudziądzu" is in the locative case, again showing location due to the preposition "w".
Spotkaliśmy się na konferencji w Grudziądzu.
We met at a conference in Grudziądz.
Here, "Grudziądzu" is used in the locative case to indicate the place being referred to with the preposition "w" ("in").