Surface

Antonyms of surface:
overhead, subsurface, underwater, submarine, subterraneous, belowground, submerged, subterranean, submersed, underground, undersea, deep, deep-seated.
Examples of usage:
  1. Watching him closely, she could see that he was far more deeply moved than appeared on the surface.
    "The New Tenant", E. Phillips Oppenheim.
  2. He then lay motionless upon the surface, at rest from all trouble.
    "Journal of an African Cruiser", Horatio Bridge.
  3. There was, however, nothing beneath the surface.
    "Masters of the Wheat-Lands", Harold Bindloss.