Some tunnel back into a place of exile
I believe the answer is:
elba
'a place of exile' is the definition.
(I've seen this before)
'some tunnel back into' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ELBA' can be found hidden inside 'tunnel back into'.
(Other definitions for elba that I've seen before include "Napoleon exile island" , "Bale out of the Mediterranean island" , "Island of Napoleon's first exile" , "Napoleon prison isle" , "Where emperor was confined" .)