Closed sunken courtyard diagram

Quick answer：

A closed sunken courtyard, also known as an enclosed courtyard or sunken garden, is a garden or courtyard that is surrounded by buildings or walls, creating a secluded space below ground level. These courtyards are often found in traditional Chinese architecture, where they serve as a retreat from the hustle and bustle of the outside world. They are characterized by their quiet, serene atmosphere and are designed to incorporate elements of nature, such as plants, water features, and sometimes even a small pavilion or gazebo.