The Nemo subs have little fans located somewhere by the portholes blowing cool air in your face during the entire ride. I know they do, because I've been on it several times and each time I was grateful for the air blowing in my face during the ride and thinking that if they didn't have the air blowing in my face and everyone else's faces that we would all most likely start feeling hot, sick, and clausterphobic. But I was leaning way in toward the porthole. Perhaps those sitting back with their faces further away from the porthole can't feel the air.