This is the 17116th most frequent Russian word.
ставшем
"Stavshem" is the instrumental singular form of "ставший," meaning "having become" or "become."
The word 'ставшем' is used here as a past participle, describing the city which has transformed into a cultural center.
В городе, ставшем центром культуры, проходят фестивали.
In the city that has become a cultural center, festivals are held.
Here, 'ставшем' qualifies the country, which has transitioned into a new home for the visiting person.
Он посетил страну, ставшем для него новым домом.
He visited the country that became a new home for him.
In this sentence, 'ставшем' is used to describe the park, emphasizing its pivotal role as a city symbol.