Once you reach the area called END
*** Spoiler - click to reveal *** After Dr. Faust dies, choose NOT to drink the potion. Solve the pilar puzzle to release the golem who will help you clear the last remaining ivy. Continue up the path and at the top approach and interact with the large black and white pulsing mass. There is a scene and the game ends.
The walkthrough has a detailed guide to solve the puzzle.