Walk down the stairs around the elevator to the open shaft, fire a portal at the bottom of the shaft and jump through it to launch yourself to the next door.
Once you're at the top, fire a portal onto the angled surface above the vitrified test chamber doors to the left. Enter the elevator and press the red button to activate it. Walk through the sliding door, past a couple rooms, and back outside. Fire a portal onto the angled portion of the support below, then jump through a portal on the ground. Portal up to the metal platform on the top right side of the back wall. Once in the lobby, your goal is to launch yourself through the circle of the giant hanging Aperture logo. Portal through the doorway and pull the lever at the end of the hall. After entering the hatch, move down the metal walkway until you reach a broken door.
