I think the song means just what it says - a man or a group of men discover a sanatorium(hospital) in an unexpected place, where blind girls are kept and treated.
These plainly dressed blind girls secretly come out every night and dance to scratchy old music to make their grim lives a little happier. These men join them in this surprise rendezvous, offer them wine and have a good time.
However, soon it's time for the girls to leave - the music fades and they sadly crawl back to their prison.
I think the song means just what it says - a man or a group of men discover a sanatorium(hospital) in an unexpected place, where blind girls are kept and treated. These plainly dressed blind girls secretly come out every night and dance to scratchy old music to make their grim lives a little happier. These men join them in this surprise rendezvous, offer them wine and have a good time. However, soon it's time for the girls to leave - the music fades and they sadly crawl back to their prison.