Continue to the right and onto the solid ground. Near the wall you will see a mine cart with a ladder on top of it. Push the mine cart down the hill and climb up the ladder. When you approach the glass, jump over the stopper at the end and try to land on the glass dome.
Doing so successfully will cause the glass to break and you will fall through.
Ride the slope down and as you near the bottom, jump across to the light on the left. From here, jump to the second light and then quickly over to the hose dangling to the left before the light fitting collapses. The hose will reel out slowly and safely lower you to the ground.
After you hit the ground, run over and knock down the scaffolding on the left. Then run to the right, you will be beset by another brain slug. Follow its direction all the way to the left, then from the beam of light back to the right and back to where it attached itself to you.
Continue to the right and drop down to the platform below, continue past the lift and two switches along the lower path.