This is the 7415th most frequent Polish word.
kolejowe
"Railway" or "rail-related."
The word 'kolejowe' is an adjective derived from the noun 'kolej', meaning 'railway'. In this sentence, it modifies 'stacja' to specify it as 'railway station'.
Stacja kolejowe jest zatłoczona.
The railway station is crowded.
Here, 'kolejowe' is used as an adjective to describe 'zabytki'. Together, they indicate that the monuments are related to railways.
Podczas naszej wycieczki odwiedziliśmy zabytki kolejowe.
During our trip, we visited railway monuments.
In the sentence, 'kolejowe' modifies 'linie', indicating that the lines in question pertain to the railway system.