The 'Tian Cheng sunken courtyard floor plan' refers to a plan of a sunken courtyard design at Tian Cheng, a traditional Chinese architectural feature. Sunken courtyards are characterized by a lower level surrounded by walls or buildings, creating a more intimate and secluded space. In a floor plan, these would be depicted with dimensions, architectural elements, and structural details to illustrate the layout and design of the courtyard.