The most nervous I ever was, was when the door on my C152 became open.
So being inquisitive, I pushed it open as far as it would go against the windflow, and had a look under the fuselage, as you do... I then realised that all that was between me and the 3000ft drop was a thin 1/16 inch of alloy sheet.... Gave me some cause for concern for the rest of the flight.