Why Am I Here
Head towards the place where the Sniper Rifle spawns, then head for the end of the path. Once you have made it to the end of the path, jump past the dead end. On the right side, there should be a place that you can jump onto. Then, there are some rocks that you must push down. Where the big one used to be, there should be writing that says "Why Am I Here?" and a signature that reads "Not Sid". The message can be hard to read clearly. If you experience difficulty, look at it from different angles until you can read it.
The easter egg is a reference to the Rooster Teeth series Red vs Blue, in which the first episode is called "Why are we here?"