This is the 12475th most frequent Portuguese word.
subterrâneas
"Subterrâneas" means "underground" or "subterranean" in English.
Here, "subterrâneas" modifies "cavernas" (caves), indicating that these caves exist below the surface of the earth.
As cavernas subterrâneas são fascinantes.
The underground caves are fascinating.
In this sentence, "subterrâneas" describes "passagens" (passages), specifying their location beneath the surface.
A cidade possui passagens subterrâneas para pedestres.
The city has underground passages for pedestrians.
"Águas subterrâneas" in this context refers to "waters" that are located underground, emphasizing their geographical placement.