Return to the Gift Shop
You'll find yourself right back where you started - the Gift Shop.
Speak to the Shopkeeper to get the novelty size key again.
Unlock the door and proceed through the level again. There are no puzzles this time - just trod on through.
When you reach what used to be a waterfall, be careful. Take your time dropping down the now volcanic area.
You're now back in the area where you collected the three trinkets. Guess what? There are three more to collect. They're all in the same spots, so retrace your steps to pick up these new key items.
Return to the Shopkeeper with these trinkets, and he'll let you out of the cave one at time. Climb the long ladder to freedom, your final Cave Paintings, and the end of the game.