The Forbidden City had become almost silent, since Aeris had passed on from this world. Only being disturbed by the nature living in the forest.
The last great disturbance, the city had seen. Was when Kadaj and his two brothers settled there while trying to bring about the Reunion with Sephiroth.
At his most suffocating times, Cloud like to take a stroll through the forest to feel closer to Aeris and Zack. As the church in Midgar’s old sector 5, has become a popular place for local civilians to visit.
Thus, Cloud visits the Forbidden City for a time to get peace and quiet away from city life. Because, although he has accepted the peace the world now has from Sephiroth. And has come to terms with himself and his inner thoughts and memories of the past. Involving Sephiroth, Zack and the experiments that Hojo performed on him.
The peace and quiet offered throughout the Forbidden City, feels far older than the current peace offered around the world. It allows Cloud to relax and believe for a time that he lived in another time and place, rather than his current location and time.