Going into a dark room and thinking? (10,3,4)

I believe the answer is:

developing the mind

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'thinking?' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'going into a dark room and' is the wordplay.
I cannot really see how this works, but
'into' could be 'in' and 'in' is found in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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