This is the 9395th most frequent Russian word.
тобольск
Tobolsk is a city in Russia, located in the Tyumen Oblast in Siberia.
In this sentence, 'Тобольск' serves as the proper noun indicating the city to which the speaker is traveling.
Я поеду в Тобольск на следующей неделе.
I will travel to Tobolsk next week.
Here, 'Тобольск' functions as the subject of the sentence, again as a proper noun.
Тобольск - это один из старейших городов Сибири.
Tobolsk is one of the oldest cities in Siberia.
In this sentence, 'Тобольска' is used in the genitive case, showing possession or relation (the history of Tobolsk).