The most common and most likely answer to this crossword clue is the 12 letter word MOUNTAINEERS
I've seen this crossword clue in The Times
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More clues leading to the result MOUNTAINEERS
Buddy explains!
The straight part
We know that "those on the way up, perhaps?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case those on the way up, perhaps? = mountaineers.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 MOUNTAINEERS mean?
MOUNTAINEERS noun- A person who climbs mountains for sport or pleasure.
- A person who lives in a mountainous area (often with the connotation that such people are outlaws or uncivilized).
- An animal or plant that is native to a mountainous area.