In hotel, immersed in a large volume (2,4)
I believe the answer is:
at home
'in' is the definition.
(I've seen this before)
'hotel immersed in a large volume' is the wordplay.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'immersed in' is an insertion indicator.
'large volume' becomes 'tome' (I've seen this before).
'a'+'tome'='atome'
'h' going within 'atome' is 'AT-HOME'.
(Other definitions for at home that I've seen before include "Oh mate! (anag)" , "Comfortable - in one's own country" , "Reception in one's own abode" , "Where one lives" , "Familiar with" .)