This is the 2570th most frequent Polish word.
rosją
"Rosją" means "Russia" in the instrumental case in Polish.
In this sentence, 'Rosją' is in the instrumental case, indicating Russia as an entity involved in the context of bordering.
Polska graniczy z Rosją na wschodzie.
Poland borders Russia to the east.
Here, 'Rosją' is used in the instrumental case, describing the country of Russia as an aspect of fascination.
Jestem zafascynowany literaturą rosyjską i Rosją jako krajem.
I am fascinated by Russian literature and Russia as a country.
In this use, 'Rosją' is instrumental, highlighting the location through which the traveling occurred.