Story related, can't be missed. You need to find the curved pipe to obscure the stone masks view. First you will need to get the waterfall working. You will need to find three turtles for this. One is by the waterfall, behind you when you enter the scene. Throw the rubber ball you have through the hoop by the episode exit for a second, and the third is in the netting in the roof of the room with the mask in. Use the spear to knock this down. Once you have these, you will start the waterfall and have access to the glyph. There is a key with the glyph which opens a door in the mask room. This is an item finding game, and you will get the curved pipe as a prize when you complete. Place the curved pipe on the steam vent for this one.