Sentence:  It was amazing how they had herded together for protection : an enormous matriarch in a quilted silk wrapper , rising from the breakfast table ; a gross boy in his teens , shuffling in from the kitchen with a sandwich in his hands ; a girl in her twenties , fat and sullen , descending the marble <WSD>staircase</WSD> ; then all four gathering on the sofa to face the inquisitor . 
Meaning of the word marked with <WSD> tags:  a way of access (upward and downward) consisting of a set of steps