The most common and most likely answer to this crossword clue is the 7 letter word ENCODES
I've seen this crossword clue in The Daily Telegraph
E
N
C
O
D
E
S
Buddy explains!

The straight part
We know that "Creates a secret passage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case creates a secret passage = encodes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ENCODES mean?
ENCODES verb- To convert (plain text) into code.
- (communication) To convert source information into another form.
- To constitute the code necessary for the biosynthesis of a protein by means of a matrix so as to transcribe DNA material.