The vast hall of darkness was much too long for Gilligan to successfully roll the apple all the way to the other side. Knowing this, he decided to walk back to exactly where he came from. Taking the exact same straight path through the darkness. 

On the floor, a few meters away from the previous door, he found the apple. Gilligan picked it up and examined it closely. All the same cuts where there, along with that small bruise on the side. It was his apple alright. 

And so with the mystery of the left door seemingly solved, Gilligan took a bite out of his delicious fruit. He then pondered his next move. Gilligan could either go through the middle door or the right hand door. Of course he could also ascend the stairs and leave the dungeon. That was always a choice.