Several years ago while shooting an event at a local college I moved back into a doorway to frame a shot. Looking up I noticed the curved entrance portal framing the sky and was captured by the strength of the image. Perspective is key, and serendipitous shots can prove powerful if allowed to happen.
Nikon D200, f/8, 1/80 second, ISO 200. Sigma 10-20 f4-5.6.