Images created using in-camera multiple exposures. It can be a bit of hit and miss affair, but when it works you get a unique image. Scenes with strong contrast and simple shapes work.
There are various techniques that you can employ. Being able to operate your camera upside down, shooting out of focus, combing long and short exposures.
The element of chance is one of the attractions. I like the way my D800 has input into image creation.
Set up your tripod and slow down, or just hand hold and see what happens when you combine a long exposure and camera shake. Long exposures show an alternative reality, the camera sensor becomes your sketchpad.
Subjects like water and lights are great subjects to explore.
A variation on the long exposure when you slowly or quickly zoom your lens to create an abstract accelerate to warp speed type of image.