I need help deciphering this sentence from a book:
"Even from this distance it appeared as an impossibly slender thread, a thread hanging in that submerged straw of a stairwell. It wavered slightly in the wake she was causing, almost as if saying goodbye."
Not sure how that the bolded "that" works in the sentence, is it describing the thread and what exactly is a straw of stairwell? How does "in the wake" work in this sentence?