Bedrock

Bedrock is an unbreakable block found at the bottom of the map. Typically generated to prevent players from falling out of the world, Bedrock is unobtainable and uncraftable.

Bedrock can also be found at the very top of the Nether, creating the impression that the Nether exists underneath the Overworld's Bedrock.

The only other place to find Bedrock is in the End, where each Obsidian pillar contains a single block of Bedrock at the top.