Place of safety unknown in a squalid urban area (6)
I believe the answer is:
asylum
'place of safety' is the definition.
(an asylum is a sanctuary)
'unknown in a squalid urban area' is the wordplay.
'unknown' becomes 'y' (algebra).
'in' means one lot of letters goes inside another.
'squalid urban area' becomes 'slum' (I've seen this in another clue).
'a'+'slum'='aslum'
'y' placed inside 'aslum' is 'ASYLUM'.
(Other definitions for asylum that I've seen before include "hostel" , "Place of safety or protection" , "sought by immigrants" , "Shelter for refugees" , "Sanctuary or institution for mentally ill" .)