Bar with underground passage leads to secure garage
I believe the answer is:
lock up
'secure garage' is the definition.
(I've seen this before)
'bar with underground passage leads' is the wordplay.
'bar' becomes 'lock' (I've seen this in other clues**).
'with' means one lot of letters go next to another.
'leads' suggests taking the first letters.
The initial letters of 'underground passage' is 'up'.
'lock'+'up'='LOCK-UP'
'to' is the link.
(Other definitions for lock up that I've seen before include "Immure" , "Cell for prisoners" , "Jail; type of garage" , "Secure garage" , "quiff perhaps?" .)