This is the 1039th most frequent Polish word.
wisły
"Wisły" is the plural form of "Wisła," meaning "Vistula," the name of Poland's longest river.
The word 'Wisły' in this sentence is used as the name of the Vistula river, demonstrating proper noun usage in the nominative case.
Wisły to piękna rzeka przepływająca przez Polskę.
The Vistula is a beautiful river flowing through Poland.
Here, 'Wisły' is used in the genitive case to indicate possession or relationship, describing the waters belonging to the Vistula.
Pływam kajakiem po wodach Wisły w słoneczne dni.
I kayak on the waters of the Vistula on sunny days.
In this sentence, 'Wisły' is in the locative case, describing location — specifically, on the shore of the Vistula.