This is the 4478th most frequent Polish word.
kolejowych
"Railway" or "related to railways."
Here, "kolejowymi" is an adjective describing "pociągami" (trains), specifying that they pertain to railroads.
Podróżowaliśmy przez kilka dni pociągami kolejowymi.
We traveled for several days by railroad trains.
In this example, "kolejowi" is an adjective modifying "pracownicy" (workers), indicating their affiliation with the railway.
Pracownicy kolejowi są odpowiedzialni za bezpieczeństwo pasażerów.
Railway workers are responsible for passenger safety.
Here, "kolejowe" is an adjective describing "zabytki" (monuments), referring to their association with the railway.