Hollow chamber (4)
I believe the answer is:
cave
(Other definitions for cave that I've seen before include "Watch out" , "Subject of speleology" , "Large grotto" , "part of rocky coastline?" , "Natural subterranean opening" .)
I believe the answer is:
cave
(Other definitions for cave that I've seen before include "Watch out" , "Subject of speleology" , "Large grotto" , "part of rocky coastline?" , "Natural subterranean opening" .)