This is the 11290th most frequent Polish word.
helskie
"Helskie" refers to something related to Hel, a town or the Hel Peninsula in Poland.
In this sentence, 'helskich' is used with feminine plural noun 'restaurants', describing them as belonging to or being related to Hel.
W restauracjach helskich serwują świeże ryby.
In the Hel restaurants, fresh fish is served.
Here, 'helskiej' as a possessive case (locative) refers to the trip's connection or association with the Hel region.
Moje wspomnienia z podróży helskiej są niezapomniane.
My memories from the Hel trip are unforgettable.
Here, 'helskie' is an adjective derived from 'Hel', the name of a geographical location in Poland ('Hel' peninsula), describing something related to or characteristic of Hel.