NICHE n.
A cavity, hollow, or recess, generally within the thickness of a wall, for a statue, bust, or other erect ornament. hence, any similar position, literal or figurative. Images defended from the injuries of the weather by niches of stone wherein they are placed. Evelun.
PIPE n. 3 definitions
Any long tube or hollow body of wood, metal, earthenware, or the like: especially, one used as a conductor of water, steam, gas, etc.