This is the 9686th most frequent Russian word.
чехию
"Чехию" is the accusative form of "Чехия," meaning "Czechia" or "the Czech Republic" in English.
Here, 'Чехии' is used in the genitive case, as it indicates possession or relation in 'посещение Чехии' (the visit of Czechia).
Мы планируем посещение Чехии этой осенью.
We are planning a visit to Czechia this autumn.
The word 'Чехии' in this context is used in the prepositional case, as it follows the preposition 'о' (about) to indicate the content of the book.
Я купил книгу о Чехии в книжном магазине.
I bought a book about Czechia at the bookstore.
Similar to the previous sentence, 'Чехии' is used in the prepositional case because it follows the preposition 'о', which governs this case.