From A Wiki of Ice and Fire
Flea Bottom is what the slum area of King's Landing is called. A down-trodden area of town. It has pot-shops along the alleys where one can get a 'bowl o' brown.' It has a stench of pigsties and stables, tanner's sheds mixed in with the smell of winesinks and whorehouses. It is a maze of twisty, unpaved alleys and cross-streets below the Street of Flour on the way down the west side of Rhaenys's Hill. The buildings lean over the narrow alleys, almost touching.