Underground shelter for trapped clubmen (6)

I believe the answer is:

bunker

I'm a little stuck... Click here to teach me more about this clue!

'underground shelter' is the definition.
'bunker' can be an answer for 'shelter' (I've seen this before). I'm unsure of the 'underground' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for bunker that I've seen before include "Sandy hazard on golf course" , "Underground shelter, store" , "Underground shelter - golfing hazard" , "Golfing 1 ac" , "at the golf club?" .)

I've seen this clue in The Globe and Mail.

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