Completing the Easter Egg will require you to locate 5 items and to bring them to the "alter room". You will recognize the Alter room as the room with 5 pedestals, a statue, two levers hidden behind a force field, and a large laser. Though note that this isn't the only room with a laser in the game, the other being the location I will refer to as the lab. This walk through will instruct you on the location of each item and the alter they correspond too.

Starting the search: When beginning your search it's best to start from the "four doors room", you'll recognize this room as the concrete room with four doors and a small pool in the middle. This room branches out into every other room on the map, making it easy to orient yourself

Computer: The computer is the hardest to find, it looks like the standard hl2 monitor model, but displaying binary code and emitting a beeping noise. It is located underneath the spiral staircase leading to the coastal area. If you're having trouble finding it, start at the four door room and go through the door with the push handle, then simply enter the building behind it, and the computer will be located there. Once you have the computer, put it on the upper pedestal to your right as you enter the alter room

Television: The television is easy as it's out in the open. It looks like the standard hl2 television model but displaying static, and emitting a distorted voice. It's located at the coastal area, sitting on the railing of a gazebo on top a spire. You'll have to do a bit of platforming to reach it. Once you have the television, place it on the lower pedestal to your left as you enter the alter room

Clock: The clock is located in the same general area as the television. Directly opposite to the Gazebo in the coast area you can enter a small warehouse with a traitor tester. Opposite to the traitor tester is a little shed housing wooden boxes, on top that shed is a small clock emitting a whistling noise. Once you have the clock, it goes on the lower right pedestal in the alter room

Picture: The picture is a small picture frame with a picture of Eli and Alyx on it. It's located in the other room with a laser, the lab. You can find the lab by going through the blue door in the four doors room and entering the door parallel to it. You'll know when you're there as everything will appear as though it's on its side and there will be a large green laser. Once you're in the lab, the picture will be sitting next to the machine generating the laser. It will be hard to hear over the machine noises, but the picture will emit a sound like someone softly crying. Once you have the picture, put it on the center most pedestal in the alter room.

Doll: The doll is the most dickish of the items. If you've played any gmod horror maps you'll recognize the model, it's the standard creepy baby doll model everybody uses. It's actually located inside the alter room itself. It's ontop the concrete frame surrounding the main entrance to the room. Once you have it, it goes on the upper right pedestal

Now that you have all the items all you have to do is pull one of the levers and see what happens. Hope this helps!