The Void

The Void
Type	Dimension
First Appearance	Pre-Release

The Void is an area in Minecraft found beneath the bottom-most layer of Bedrock in the Overworld and in the Nether, or falling of a cliff in The End.

Purpose

Players who fall into the Void suffer an instant death in Survival Mode. In Creative Mode, it was possible for Players to die prior to Update 0.11.0. The Player cannot build in the Void.

Accessing

Creative Mode

In Creative Mode, Players must first reach the layer of Bedrock and then dig through it in the Overworld or in the Nether. They will fall into the Void and keep falling unless they start flying or fall onto Invisible Bedrock. In The End, something pretty similar occurs, but it's naturally Air all through the Void..

Survival Mode

One way the Void can be accessed in Survival Mode in the Overworld or in the Nether is by breaking the Bedrock layer on Creative Mode and switching back to Survival Mode. Another is when Generated Structures spawn near the Bedrock layer, thus replacing some Bedrock. The Player can just mine the Blocks to access the Void.  In The End, there is no need for that, the passage is air naturally.

Trivia

• Mobs will die too if they fall into the Void.
  • It is nearly impossible to make Endermen fall into the Void as they will teleport away.
• In Superflat Worlds, the Player cannot see the Bedrock layer at the Invisible Bedrock. But if the Render Distance is high enough, in other world types, the Bedrock is visible.
• Items will disappear once they enter the Void. 
• If the Player generates a world on a version of Minecraft which only has Old Worlds, and then upgrades the game to one with Infinite Worlds, and then converts the Old World to an Infinite World, there would be large square pits outside the boundaries of the Old World that lead to the Void. 
• Prior to the Nether update, the Void can be accessed by using a Nether Reactor, with the Netherrack replacing the bedrock. A video of it can be seen here.