This is the 752nd most frequent Persian word.
سمنان
Semnan: A city in northern Iran, and the capital of Semnan Province.
In this sentence, 'سمنان' refers to the name of a city in Iran.
سمنان یکی از شهرهای ایران است.
Semnan is one of the cities in Iran.
Here, 'سمنان' indicates the destination of the speaker's travel.
به سمنان سفر کردهام و مردم آنجا مهربان بودند.
I have traveled to Semnan, and the people there were kind.
In this usage, 'سمنان' highlights the geographical and natural attractions of the city.