Why is Chengde City a summer resort? Isn’t nearby Qinhuangdao cooler?

This has nothing to do with temperature. . . Chengde Summer Resort is a royal garden built during the Kangxi period. It is the largest royal garden in northern my country. It is called a summer resort because the emperor came to Chengde every summer to escape the summer heat. . . Besides, the emperor led the Eight Banners soldiers to hunt at Mulan Paddock in Chengde and passed by Chengde. If the Emperor had led the Eight Banners soldiers to Qinhuangdao for fishing, maybe Qinhuangdao would also have a summer resort, hahaha. . .