This is the 10760th most frequent Polish word.
duńska
"Danish."
Here, 'duńska' is an adjective describing the noun 'kawiarnia', indicating its origin.
To jest duńska kawiarnia.
This is a Danish coffee shop.
'Duńską' here agrees with the feminine, singular noun 'kulturą' and is in the instrumental case due to the preposition 'się' with the verb 'interesuję'.
Interesuję się duńską kulturą.
I'm interested in Danish culture.
In this sentence, 'duńską' is the feminine, singular, accusative form of the adjective, matching the grammatical case of the noun 'porcelanę'.