Vivian Nightsong is standing in the middle of the plaza, playing her harp and entertaining the crowd. She spices her performance up with small jokes and anecdotes from her recent trips down into the sewers. It's quite possible that the latter is the reason why a large part of the crowd is listening so intently. Any news of the dungeon attracts attention, and Vivian knows this.
And so she plays her harp, singing Journey To The Lowest Place On Earth.
After some polite applause, shouts from the audience ask what the lowest place in the dungeon she has been are. An obvious dig for information. She turns it into a joke, saying what while she hasn't been too deep, her companions have been deeper. She tells the story of the swashbuckler jumping into the sewage (and thus ending up lower than she was).
And some warning about the dangers of piranhas in the sewers provide a perfect segue into her next song, Dangerous.