And the opposite of that is the BCM, where if you're late starting the climb up towards the YH at Pen-y-Pas you see flashing lights in the sky and assume they are aerials on top of the mountain, or low flying aircraft, before the horrible realisation hits that they are bicycle lights and you need to get up there...
(not that the climb is hard, but they seem an awfully long way up when you are at the bottom)