This was taken in Portugal in the sea caves near Lagos. I was in a boat similar to this one which was bobbing from the wake. I was particularly struck by the lighting and hues of turquoise and the man ducking his head added to the sense of movement. As it was dark in the cave, I was lucky to not to get too blurred a shot as I was shooting at 1/50s from a moving position. Lens used - Canon 24-105 f/4L IS.

Some of the other contenders are here.