Warnings Active: Cube Dispenser, Cube Hitting Head

The cube-dispensing tube drops the cube necessary to open the door into a pit. Shoot a portal into the pit, underneath the cube; if the cube is not in a position to fall through (because of the grating on the edges of the pit) jump in and manually push the cube into the portal. Note the redirection of movement that accompanies falling down into a pit and coming out sideways.

Portal Walkthrough