This is the 486th most frequent Polish word.
turystów
The word "turystów" in Polish means "tourists" in English (genitive or accusative plural form).
In this sentence, 'turystów' means 'tourists' and is in the genitive plural form, used because of the verb 'odwiedza' indicating the visiting of the city.
Wiele turystów odwiedza Kraków każdego roku.
Many tourists visit Kraków every year.
Here, 'turystów' is in the genitive plural form used after the verb 'nie widziałem', which requires it due to the negative construction.
Nie widziałem jeszcze tylu turystów w tym miejscu.
I haven't seen so many tourists in this place before.
In this example, 'turystów' is in the dative plural form to indicate the group to whom the guide is speaking.