The most common and most likely answer to this crossword clue is the 11 letter word PERAMBULATE
I've seen this crossword clue in The Times
P
E
R
A
M
B
U
L
A
T
E
Buddy explains!

The straight part
We know that "Walk" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case walk = perambulate.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 PERAMBULATE mean?
PERAMBULATE verb- To walk about, roam or stroll.
- To inspect (an area) on foot.