Poseidon's place (3)
I believe the answer is:
sea
'poseidon's place' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sea that I've seen before include "The drink" , "The deep" , "Division of an ocean" , "E.g. Yellow, Red area" , "Caspian, e.g." .)