The APOD description for May 4, 2010 of the first picture below reads:
"If you tried to enter this hall of fog, you would find it dissipates around you. The hall is actually an optical illusion created by sunlight backscattering off of a cloud passing below the peak of the mountain from which this picture was taken. Known as a fogbow and similar in some ways to "the glory", the phenomenon is sometimes seen from airplanes. The ring's center appears near the image bottom where the shadow of the photographer is visible. This shadow would likely change as clouds passed, creating a faux moving giant known as the Brocken Spectre. In the picture, several concentric rings of the fogbow appear to create a hall for this mountain king. The cause of fogbow supernumeraries arcs and glories have only been understood recently and are relatively complex. Briefly, small droplets of water reflect, refract, and diffract sunlight backwards towards the Sun. Atmospheric backscattering phenomena have a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called the gegenschein."
APOD mention of the Brocken Spectre Giant reminded me of this:
Another image of a fogbow (cloudbow) taken from Taburiente's caldera edge
It's amazing how a cloud passing by can create such beautiful phenomena: I was completely engulfed in the clouds just a few moments after taking this picture. Some more seconds and it was all clear again!