One Minecraft creator has rebuilt Portal 2, using the tools available to every player.more
A Minecraft player by the name of Lag Master163 put together the Portal 2 map featured in the video below. It's still in beta, and is the result of about one month's work.
You can download the build here and use it to make your own, apparently, but we haven't tried so can't comment on the contents.
I'm amazed this was created in vanilla Minecraft (with texture packs), as opposed to via mods. It's actually pretty interesting to read other player's guesses as to how the recreation was put together.