This is the 4857th most frequent Polish word.
ostrowskim
"Ostrowskim" is the locative or instrumental form of "Ostrowski," meaning "related to Ostrów" (a place name) or "Ostrowski" (a surname) in Polish.
Here, 'ostrowskim' functions as an adjective describing 'folklorem,' connecting it to Ostrów.
Interesuję się ostrowskim folklorem i tradycjami lokalnymi.
I am interested in the Ostrów folklore and local traditions.
In this context, 'ostrowskim' is an adjective modifying 'krajobrazów,' emphasizing their regional origin from Ostrów.
Piękno ostrowskim krajobrazów zachwyca każdego odwiedzającego.
The beauty of the landscapes in the Ostrów area amazes every visitor.
In this sentence, 'ostrowskim' is used as an adjective describing the district ('powiatem') of Ostrów.