By killing the Wither, you have 1/3 chance to get a Ghost Stone.
When using this ghost stone (with a left click), you will pass in ghost mode for a short time. In ghost mode you go in the direction that you were looking and you are able to pass through the walls. You can manually leave ghost mode by sneaking.

You can add the Ghost View enchantments on your helmet by dropping it and a wither skeleton skull on an anvil.
Ghost View give you the ability to see particles arround ghosts.