2. Portal 2's Half-Life (3?) Area
https://www.youtube.com/watch?v=--hRLz6Xi0Q Who says Valve aren't thinking of doing more Half-Life any time soon? Certainly not the wing of developers who put together Portal 2, as although it'd take some sort of out-the-box-thinking genius to figure out, you can come across the 'wreckage' of HL2's mysterious Borealis research ship if you know where to look. It's essentially quite easy to find if you're already someone who pokes around every nook and cranny in a given location, as a hidden door in the corner of a particular command room (shown above) in Chapter 6 will then take you out onto a landing, where the Borealis life ring sits nicely on the side. Naturally this has caused fans to use it as 'confirmation' Half-Life 3 is in the works, but being that Portal 2 released in 2011 and there's been nay a sniff of anything else from Valve, it's most likely just a knowing wink to those who've played Episode 2.