This is the 11834th most frequent Polish word.
kościołów
"Kościołów" means "churches" (genitive plural form) in English.
Here, 'kościołów' is the plural genitive form of 'kościół' (church), used after 'wiele' (many), which requires this case.
W naszym mieście jest wiele starych kościołów.
In our city, there are many old churches.
In this sentence, 'kościołów' is also in the plural genitive case, as it follows the word 'kontury' referring to their collective delineation.
Kontury kościołów rysowały się na horyzoncie.
The outlines of the churches were drawn on the horizon.
'Kościołów' is again in the plural genitive case, as it follows 'najpiękniejszych', which describes the adjective to mean (of the churches).