I know that they're passages where air can pass through. But most diagrams of the passages don't help me visualize them at all. They look like a second hole through the head, and that's not what they really look like (are they really almost as wide as the mouth? What about their height?). They always seem closed if I try to insert something in - I can, of course, push harder, but I don't try for fear that I may severely irritate my nasal passages (which could have very unpleasant consequences). All I know is that i can fill them up with a fair amount of water (maybe even more than I can hold in my mouth) with those NeilMed sinus rinses. I know that an endoscope could easily solve the question, but I can't find any pictures of an endoscope going through the nasal passages.