In "Solo Leveling," the dungeons and the monsters within them play a crucial role in the development of the characters. The constant challenges and battles against powerful foes within the dungeons force the characters to grow stronger, both physically and mentally. These encounters often push the characters to their limits, leading to character growth, new abilities, and a deeper understanding of themselves and their powers. The dungeons also serve as a stage for character interactions, showcasing their relationships, teamwork, and personal growth throughout the story.