This is the 597th most frequent Czech word.
kremlu
"Kremlu" is the locative case of "Kreml," meaning "Kremlin" in English, referring to the fortified complex in Moscow or similarly named locations.
In this sentence, 'Kremlu' refers to the Kremlin as the subject of the exhibition, showing the locative form used to specify about what the content of the subject is.
Navštívili jsme výstavu o historii Kremlu.
We visited an exhibition about the history of the Kremlin.
Here, 'Kremlu' appears in its locative form to indicate the place where the situation took place.
Politici jednali o situaci na Kremlu.
The politicians discussed the situation in the Kremlin.
In this sentence, 'Kremlu' is used in the locative case referring to its location in relation to the tourists.