Back in the day, coal fires had to be kept burning all day and all night in large libraries and in order to be fed round the clock someone had to live inside the library. These large spaces were designed to be the homes of the coal stokers and their families. Many libraries had these apartments upstairs or somehwere on the premises, which today are pretty large by modern New York City standards.
But, as coal became obsolete, and central air became the norm, these apartments became useless and were eventually shut up. While it can be sad to think of them going empty, a few are of these derelict and unused apartments are now being converted into public spaces, perhaps reading rooms or computer stations. These apartments may have been left behind by progress, but perhpas some of them can have a new life. Who knows what the future will bring for these apartments? Have a look in the video below from Atlas Obscura.