Since urological or gynecological exams rarely result in any sexual arousal and unwanted sexual advances produce only revulsion, it is safe to say that the ultimate erogenous zone in both males and females is

mind

Explanation:

An area present in the body that is highly sensitive and thus the stimulation of which may result in sexual arousal is termed as an erogenous zone. There are different erogenous zones present in the body an all these zones vary in their sensitivity and these zones mainly provide a sense of pleasure upon stimulation. However, the ultimate erogenous zone is the mind and one can say that it is a hidden erogenous zone as it is not exposed to tactile sensations like the other areas. This is the reason why during urological or gynecological exams or unwanted sexual advances a person doesn't get sexually aroused even though the same areas are being touched.

It should be cryosphere and hydrosphere