unfathomed
1. [ adjective ] situated at or extending to great depth; too deep to have been sounded or plumbed
Synonyms: unplumbed unsounded profound
Examples:

"the profound depths of the sea" "the dark unfathomed caves of ocean"-Thomas Gray "unplumbed depths of the sea" "remote and unsounded caverns"

Related terms: deep
Similar spelling:   unfathomable
  unfattened
  unpatterned
  unfeathered