This is the 12251st most frequent Polish word.
mieleńskiego
"Mieleńskiego" is the genitive singular form of the Polish adjective "mieleński," meaning "of or related to Mielno," a town in Poland.
The word 'mieleńskiego' in this sentence is used as an adjective describing the 'region', which is in the genitive case, indicating origin from Mielno.
Mój przyjaciel z mieleńskiego regionu opowiadał mi o pięknych plażach.
My friend from the Mielno region told me about beautiful beaches.
'Mieleńskiego' acts as an adjective referring to 'natural beauty', aligning with the structure of the sentence and describing the beauty associated with Mielno.
W trakcie podróży widzieliśmy wiele mieleńskiego piękna przyrody.
During the trip, we saw much of Mielno's natural beauty.
Here, 'mieleńskiego' modifies 'castle' (zamek), placing it as pertaining to the castle of Mielno, in a genitive or descriptive role.