In Borderlands 2 for the PC, PS3, and Xbox 360, there is a hidden area in Caustic Caverns that is a big Minecraft easter egg, with Badass Creepers, and some different Minecraft skins for each character.
You can only get to Caustic Caverns once you reach Chapter Nine.
Once you reach Chapter Nine, you can get to Caustic Caverns a couple different ways, both of which are through Sanctuary Hole in Three Horns Divide.
You can either proceed through Sanctuary Hole and you’ll eventually get to Caustic Caverns, or you can take the shortcut. Near the edge of town, look for a large cliff behind a large building that drops into a large hole. Look around this area and you’ll see some ledges you can drop down into to reach Caustic Caverns.
Once in Caustic Caverns, run to the northwest area of the map and look for some tracks with mine carts on them. Travel north on these tracks until the tracks bend left a little, and there is a mine cart with a chest right in front of it on the right side of the tracks, and what looks like a glowing yellow stone to the right of the cart.
Off behind the glowing yellow stone, you’ll see a boulder that has unnaturally straight angles. Jump on top of it, and jump off to the left of it and you’ll see some familiar Minecraft dirt blocks.
Punch through the dirt blocks and you’ll come to a wall of cobblestone and coal looking blocks.
Once you’re through the cobblestone and coal wall, you’ll be greeted with an area of exploding Creepers and Badass Creepers. These guys drop a different Minecraft head and skin for each character, and have a chance to drop rare loot as well.