SPOILER:
You didn’t see it because it’s completely optional. In Red’s Tree House there’s a room beneath the carpet. Here you’ll find a character, who in exchange for help, will offer you a shortcut to the light house that doesn’t involve going through the forest. This character will request a blue light, which you get in the form of a blue-flamed candle from the candle head statue in the Sculptor’s House if you de-petrify him with a potion made in the tree house. Won’t work if you took the candle from the statue before hand.