This is the 138th most frequent Finnish word.
turun
"Turun" is the genitive form of "Turku," meaning "of Turku" (a city in Finland).
Here 'Turun' again shows possession or association, indicating the market square located in Turku.
Kävin Turun torilla ostamassa vihanneksia.
I visited the Turku market square to buy vegetables.
In this context, 'Turun' denotes that the archipelago is related to or connected with Turku.
Matkan aikana näin Turun kauniin saariston.
During the trip, I saw Turku's beautiful archipelago.
'Turun' indicates the genitive case of the place name 'Turku', specifying that the castle belongs to or is associated with Turku.