Continue to the right. You will see an elevator here.
Note: Run up to the elevator and press down. You will climb down the edge. Jump to the chain here and climb all the way to the bottom to find an egg. Step on it for the achievement/trophy - Under Ground.
Press the button to lower the elevator. Once the elevator is at its lowest point, hit the switch again ad jump onto the elevator to be lifted up to the higher platform. Hit the switch here to lower it again, then hit it a second time and jump on top to ride it up. When you reach the highest point, you will need to jump off immediately as you will be in a horizontal turrets laser sight.
The turret will break the rope holding the crate nearby and it will fall to the ground. Lower the elevator again and push the crate on top. Raise the elevator again and jump on top, standing behind the crate for safety. At the top, hop on the crate and then jump to the platform above the turret. In here you will find another gravity switch. If you turn it off, you will see a crate drop down, wait until it is moving down the slope to the right and turn the switch on and off continually until you can bring the box out of the area. Try to not let the box hit anything as this will change the direction in which it moves. Once the box is out, push it as far as possible to the right.
Jump back down to the upper platform below and lower the lift. Jump over the crate and push it to the right, there is another horizontal gun in the far right of the area and you can use the crate as cover. From the crate, climb the ladder. At the top, hit the switch to invert gravity. Jump over the box and run to the left to find the second box you liberated earlier. Push it back to the right so you now have two boxes to play with.
You should see a section of wall that moves in and out from the right hand side, we will need to utilise this to continue. Place one crate closest to the platform from which the moving wall comes out. Place the second crate further away. Run back to the switch and when the wall is below the first crate, activate the gravity reversal. The wall should have the first crate on it and should be pushing the second crate along the floor. Quickly jump up onto the second crate, then onto the moving platform, and then up again onto the first crate. From here you can jump up to the ledge on the right.
Climb down the ladder to continue.