Subterraneans is a word that is commonly used to refer to underground places or spaces. However, there are many synonyms that can be used to describe such areas. For example, the word underground can be used to describe any place beneath the surface of the earth. Other synonyms include subterranean, subterraneanly, subsurface, subaqueous, subaqueously, subglacial, and sub-aquatic. Each of these words can be used in different contexts to describe areas that are beneath the ground. Whether you are writing about caves, tunnels, or underground caves, there are many words that you can use to describe these subterranean spaces.