"山中避暑之地" can be translated into English as "a summer retreat in the mountains" or "a mountainous summer resort".
Both expressions convey the idea of a place in the mountains where people can go to escape the summer heat. The first option, "a summer retreat in the mountains," emphasizes the purpose of the place as a retreat for summer relaxation, while the second option, "a mountainous summer resort," highlights its location in the mountains and its function as a resort during the summer.