This is the easiest 'level' of the entire game. Dr. Mossman will take you to see Dr. Vance after the decontamination process, explaining what they are trying to achieve. After getting out of the lift, Dr. Vance will show you around the lab and Alyx will pop down to say hi.

Soon Alyx will take you out into the Scrapyard where you have your first encounter with the Zero Point Energy Manipulator, or more simply (and less geeky) the Gravity Gun. Alyx will give you a quick lesson on how it works and how to use it effectively. You can go nuts here without having to worry about hurting anyone, and it's hilarious to see Alyx walking around with a fresh coat of paint.

Now you get to meet the aptly named Dog. How Alyx can find a 10 foot tall, 5 ton machine cute is astounding. Perhaps it's a girl thing with machines. However, your play time with Dog is rudely interrupted by a surprise Combine attack- head back into the lab with Alyx to find out what's going on.

Dr Vance explains what's happening, then tells Alyx to get you out of there. You become separated from Alyx due to a rockfall, and Alyx tells you to go through Ravenholm to get to the other side.

Dog obligingly opens the door to Ravenholm so you can get through. You will come to an elevator shaft with a ladder leading up, but the ladder is locked shut. Open it with your crowbar and head on up to Ravenholm.