The lower layers of the ground or of a body of water.
Subsurfaces are usually hidden and not easy to see.
Examples:
The archaeologists dug into the subsurfaces to find ancient artifacts.
Fishermen use special equipment to see the subsurfaces of the water.
The roots of the tree grow deep into the subsurfaces of the soil.
The treasure was hidden in the subsurfaces of the cave.
There are many creatures living in the dark subsurfaces of the ocean.
The subsurfaces hold many secrets and surprises.