This is the 7997th most frequent Russian word.
корею
"Корею" is the accusative form of "Корея," meaning "Korea" in English.
In this sentence, 'Корею' is the accusative case of 'Корея', used as the direct object of the verb 'посетить' (to visit).
Я всегда хотел посетить Корею.
I have always wanted to visit Korea.
Here, 'Корею' appears in the accusative case as part of the prepositional construction 'в Корею' (to Korea), indicating direction.
Она мечтает о поездке в Корею.
She dreams of a trip to Korea.
In this usage, 'Корею' is accusative, functioning as the direct object of the verb 'исследовать' (to explore).