In response to Minecraft 1.8, an update that lets players create a flickering wall that borders the in-game world, a new survival mod called Captive Minecraft has been developed which places the player in a 1x1 box that expands as they earn achievements.
"For each Minecraft Achievement you get, the World Border widens by half a block in each direction," reads a statement from the mod's creators. "As your captive world slowly expands, you gain access to more and more resources. You'll have no trouble Getting Wood or Taking Inventory, but suddenly making that Cake and riding a Pig off a cliff isn't quite so simple..."
The beta version of Captive Minecraft can be found at the Farlanders website. While the 1.8 patch has yet to be released, players can download the world border feature as a test patch on Mojang's website.
You can watch the mod in action in the trailer above.