Put your camera on a tripod. Leave the shutter open for a few minutes.
It works best if you photograph water or light that is moving.
These images don't even show the cool things you can do.
Some photographers make these exposures over hours.
The easiest thing to do is use a shutter remote so you don't have to hold the shutter down on the actually camera and risk camera shake.
Lately I've been loving long exposure and multiple exposures and all that weird but awesome stuff.
Do you have any other cool techniques?
I'd love to know!