Guard house and park for knight raised around centre of Grenoble (6)
I believe the answer is:
prison
'guard house' is the definition.
'prison' can be an answer for 'guard' (thesaurus). I am not sure about the 'house' bit.
'park for knight raised around centre of grenoble' is the wordplay.
'park' becomes 'P' (abbreviation as on an automatic car's gear lever).
'for knight' becomes 'sir' (I can't justify this - if you can you should believe this answer much more).
'raised' shows that the letters should be reversed in order (going up in a down clue).
'around' is a reversal indicator.
'centre of' says to take the centre.
The central letters of 'grenoble' are 'no'.
'sir' in reverse letter order is 'ris'.
'no' in reverse letter order is 'on'.
'p'+'ris'+'on'='PRISON'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for prison that I've seen before include "Place of confinement" , "No rips (anag)" , "Correctional institution" , "Clink - jug" , "Wormwood Scrubs, for example" .)