The most common and most likely answer to this crossword clue is the 6 letter word RAMBLE
I've seen this crossword clue in The Daily Telegraph
R
A
M
B
L
E
More clues leading to the result RAMBLE
- Artist and doctor on initially leisurely evening stroll
- Run, walk, walk
- Take a long walk with thriller writer, right to the top
- Go on run and walk
- Hike or stroll beside river
- Go for a long walk with English novelist, right to the top
- Walk or stroll by river
- Stroll past river, or walk in countryside
- Walk and talk at length
Buddy explains!

The straight part
We know that "Go for a long walk" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case go for a long walk = ramble.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 RAMBLE mean?
RAMBLE noun- A leisurely stroll; a recreational walk in the countryside.
- A rambling; an instance of someone talking at length without direction.
- A bed of shale over the seam of coal.
- A section of woodland suitable for leisurely walking.
- To move about aimlessly, or on a winding course
- To walk for pleasure; to amble or saunter.
- To talk or write incessantly, unclearly, or incoherently, with many digressions.