I took this at the Palace of Versailles in France a year or so ago. It was part of an art installation there at the time and is a huge 20 foot round concave mirror reflecting the sky and depending on the angle the palace itself (you can just see some of the palace on the top edge). I makes for an interesting shot as though I have copy and pasted another piece of sky into the picture upside down.
"The fascinating moment which you wish to preserve for ever in a photo disappears as quickly as it comes; you must be prepared . It is not enough for you to know what this lever or that knob does, you must learn to handle your camera as instinctively as the pianist find his notes" Voigtländer Manual 1933