Riddle

What goes through a door but never goes in and never comes out?

Choose an answer

A.A mail slot
B.A doorknob
C.A peephole
D.A keyhole
Hint: It's a 2-word phrase with 8 letters, starting with "A".

Answer

A keyhole

Why this is the answer

A keyhole passes through the thickness of a door itself but, being part of the door, never travels in or out of it.

This riddle is filed under Hard/Difficult Riddles and rated Easy.