Possible Clues:

• As far as one can see, the zoo in H.R. is there
• Line where sky meets sea
• Line at which the sky and Earth appear to meet
• Can't see past this
• As far as one can see
• You can't see beyond it
• Detailed zoo rhino's blurred range of vision
• A slice of chorizo needed, as far as one can see
• Long-running British TV documentary series that covers science and philosophy
• Distant line