Sentence:  That subjected us to a quarantine of twenty-one days upon arriving at Genoa after a long and troublesome crossing. They gave the passengers the choice of undergoing it on board, or in the <WSD>lazaretto</WSD> in which they warned us that we would find only the four walls, because they had not yet had time to furnish it. 
Meaning of the word marked with <WSD> tags:  A ship or building used for quarantine.