Climb on the highest level, go to the right and move the lever. Ride by cable car to the left (to the end), up and then right (you can ride through the octopus room only because you set the right pattern in the rotating room). When you come to the place with dark grey circle, you need to put the line to ride through it.
Ride down to the branch below and to the circle, then go back and do this again. When the line is complete, back to the dark grey circle and go right. Ride right as you come to the second tower. Put the cable car below the circle.