Portal 2 Walkthrough: Test Chamber 05
Climb the stairs towards the door. The announcer will say that if the enrichment center is currently bombarded with fireballs, meteorites, or other objects from space, to please avoid unsheltered testing areas wherever a lack of shelter from space-debris does not appear to be a deliberate part of the test. Go through the door. Shoot a portal on the floor and fall through it to end up in a big room with a red switch and a big red pressure button.
Notice the diagram near the red switch indicating its for dropping creates. Activate the switch. A crater will drop onto the platform on the end of the room. Shoot a portal beneath the crater to have it fall near the buttons.
Take the crater and place it on the big red button. This will activate the stairs leading to a floor with a door. Climb them and you will notice another big red button along with two red switches. The switch to the left drops a crate into the water. The switch to the right raises and lowers a drawbridge.
Shoot a portal on the small platform in which the crate drops just before hitting the water.
Observe how if you press the left switch now, the crate will fall through the blue portal and emerge from the orange portal, but goes too far and still lands in water. Now press the left switch again and IMMEDIATELY press the right switch. This will raise the bridge in time to stop the crate from going into the water. Take the crate and place it on the big red button, then go through the door. The announcer will congratulate you and tell you that the enrichment center reminds you that although circumstances may appear bleak, you are not alone and that all aperture science personality constructs will remain functional in apocalyptic, low power environments of as few as 1.1 volts. Go through the barrier and board the elevator. You will have now reached test chamber 06.