Place to unburden dreadful lesson of Cain (12)

I believe the answer is:

confessional

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'place to unburden' is the definition.
I can't judge whether this definition defines the answer.

'dreadful lesson of cain' is the wordplay.
'dreadful' is an anagram indicator.
'lesson'+'of'+'cain'='lessonofcain'
'lessonofcain' with letters rearranged gives 'CONFESSIONAL'.

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(Another definition for confessional that I've seen is " Where to acknowledge sin".)

I've seen this clue in The Telegraph.

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