Grenouille's "debaucheries" take place in his inner fortress. He begins by thinking about scents from his childhood, and if his disgust at them isn't quite enough, he thinks about the smell of Grimal's tannery or the stench of thousands of Parisians in the summer. Finally his hate explodes, extinguishing all the obnoxious smells and giving Grenouille a sense of righteousness.
Grenouille is essentially masturbating by wallowing in his own hatred of humanity, as malice, scent, and sex are again mingled in Süskind’s descriptions. In hating others with this degree of intensity, though, Grenouille is seemingly able to experience some love of himself, and a sense of power over things he finds inferior or repulsive.
Afterwards, Grenouille stretches out inside his cave. In his mental fortress, he dozes and enjoys pleasant scents. In the late afternoon of Grenouille's inner world, he rises and admires his inner empire like a conqueror. Grenouille's inner self strides through the fields, sowing seeds of fragrance, and then brings on a downpour. The scents bloom like flowers and mix together, and Grenouille is satisfied with his work. All the created scents celebrate their creator with songs and more wonderful smells. When Grenouille gets tired of the celebrations, he retreats to his heart and his inner fortress.
Here, we see Grenouille's true dreams and desires. In his inner world, he has total control and can revel in his sense of smell—he can create scent and destroy it on a whim. His people celebrate him with perfumes and he's made to feel powerful. These afternoons in his mental fortress will be important later, as they will influence what Grenouille's real-world goals become.