Quest of an Obscure and Dubious Nature

Many years ago I saw a film which I do not remember the name of. It was about a woman who inhabits an apartment that turns out be be evil/gateway to Hell/some such thing/or is it? At first she fights this possibility but eventually succumbs/accepts/loses her mind. From the style and color quality of the film I would say most likely 1970-75. Maybe even filmed in New York: part of the premise was the inability of a New Yorker to turn down a good deal on an apartment--even if it's the Mouth of Hell. The cast is real small--the woman, her friend/boyfriend, the previous tenant, possibly a neighbor or cop, and that's it.
Any ideas on what film this is?

[filmmaker2]

the sentinel