Autostereogram (Magic Eye)

A special category of images which are only visible to person with two eyes. It uses an optical illusion to show a 3D image through a 2D image.

It uses the fact that brain interprets 3D objects by using the differences between the two 2D images seen by our two eyes. To watch these images you just have to push your focus behind the image such as column n seen by left eye overlaps with column n+1 seen by the right eye or use the following link
How to See 3D and Magic Eye

Some Samples:

Wikipedia

Google Search for such images

Magic Eye

Lucid Dreams

Lucid Dream is a dream where a person knows that he/she is in a dream while the dream is in progress. (Some sort of a matrix like world where the rules of normal world can be either bend or broken. Just think of possibilities.)

Its one of the wonderful things when your unconscious mind interacts with your conscious mind.

What we see or perceive is a model of the world created by our brain based on the inputs received by our senses. During a dream similar model is picked up by the brain just the input is not added from sensory organs instead given by unconscious mind mostly the thoughts the person is going through. During Lucid state we can add some inputs from our conscious mind too.

Its far more difficult to have consistent lucid dreams than the first one but a great thing to explore.

Have Fun :)

Wikipedia

Lucidity