This is an outtake from the camera movement challenge.
I used the ND 110 grad filter and moved the camera a little bit. The bright bits are the sun reflected on water.
In the challenge entry, I increased the shutter speed to 30s and rotated the camera 90 degrees with the shutter open. It's one exposure, but it looks like a double.
Such a great technique. Thanks for sharing. I quite enjoyed your challenge entry and I was thinking it looked more like an overlay. This is definitely more of a double exposure feel!