What is the tenement like on bayard street that riis describe

The tenement was the size of an triangular yard space with dim light as an average cellar.

Explanation:

(passage below)

"I counted the other day the little ones, up to ten years or so, in a Bayard Street tenement that for a yard has a triangular space in the center with sides fourteen or fifteen feet long, just room enough for a row of ill-smelling closets [toilets] at the base of the triangle and a hydrant at the apex [highest point]. There was about as much light in this “yard” as in the average cellar. I gave up my self-imposed task in despair when I had counted one hundred and twenty-eight in forty families. . . . "