Opposite words for surface:
deep, subsurface, submerged, deep-seated, subterraneous, submersed, submarine, overhead, belowground, subterranean, underground, underwater, undersea.
Usage samples:
  1. The light rose higher above the surface.
    "Paddy Finn", W. H. G. Kingston.
  2. He gave his own pilot orders to land on the surface of Eden.
    "Eight Keys to Eden", Mark Irvin Clifton.
  3. Here and there the surface lifted- bent- broke with shriekings, groanings, thunderings.
    "The River and I", John G. Neihardt.
  4. He was drawn under the water with the boat, but later came to the surface and was rescued.
    "Kelly Miller's History of the World War for Human Rights", Kelly Miller.