I believe that everyone is either a "pillow" person or a "blanket" person; one of those two you'd prefer to not do without. I am a person of the blanket variety, and so as the summer months begin and the humidity engulfs, I find myself wrestling with my sheets. It's just sometimes so hot, but I can't sleep without at least a light blanket (I know, I know...first world problem).
And so it's nights like the past few-- when it's cooler than normal-- that sleeping with the window open brings me the great joy of getting to pull on my comforter again. Throw in the purification of cool, fresh night air and the comforting rumble of a train passing and you have the makings of a perfect night's sleep.