EDIT: i was confused with something else. OK IIRC here's what happened:
In the culture at the time, if you took a guest into your house, you protected them with your life. Now the visitors had come to warn Lot and his family that the cities (neighboring cities: Sodom and Gomorrah) were going to be destroyed. The city was infamous for its residents being homosexual and raping strangers. When the mob demanded the visitors of Lot, he refused (see first sentence for reason) and offered up his daughters instead. The crowd refused the daughters: they wanted the visitors instead. The visitors (angels) struck the mob with blindness. The next day, the visitors led Lot and his family out of the city, and it was destroyed (here's the other tale, of Lot's wife, who looked back in hesitance and was turned to a pillar of salt). the city was destroyed with fire and sulfur from heaven.
there you have it.