I guess the most odd aspect to an outside observer is how incredibly indistinguishable , at least from a physical observation, caste members are from each other. This is in such stark contrast with the societal confinement it locks people into it borders on a parody on prejudice, were it not so tragic.
EDIT: This star trek episode comes to mind (Are you blind?): http://www.youtube.com/watch?v=vi7QQ5pO7_A