The moment you leave the store room, you get a call from Apple Kid, who's really excited about his surprisingly bogus-sounding invention, a Trout Yogurt Machine. He says that he has sent it via Escargo Express. You'd better go outside to receive it.
Meet a Bunch of People Outside
Before the Escargo man gets there, a monkey comes up to you and tells you that Talah Ramah, the monkey guru of the desert, wants to meet with you. After the monkey teleports away, the Escargo Express Neglected Class delivery man arrives and tells you that he lost the Trout Yogurt Machine in the desert. And then, a maid from the Monotoli building will come up to you and say that she really wants the Trout Yogurt Machine that she heard you talking about. And then she'll wander off.
Um, okay. That was a lot to take in. But it sounds like you need to go to the desert to get the Trout Yogurt Machine, so why not visit Talah Rama and see if he knows anything about it?
Go to the Monkey Caves
Get to the desert in whatever way is most convenient for you. Buy a Picnic Lunch and a Skip Sandwich. Get the Pencil Eraser from Escargo Express if you don't have it with you. And make room in your inventory. You don't really need anything other than those three things, because (thank goodness) there are no monsters to deal with in the next part.
Once you're all set, go north from the drug store. There is a monkey standing near a ladder in the ground. Climb down to find yourself in the monkey caves.
This place is a little weird (as is to be expected from a cave full of monkeys,) but it's nice and safe, and it's relatively easy to understand how it all works. Here's the deal: the doors in this cave are (for the most part) guarded by monkeys. Each monkey has a specific type of item that it wants, in exchange for moving out of the way so that you can go farther into the cave. You'll find all of the monkey trade items within the cave itself, with the exception of the Picnic Lunch and the Skip Sandwich that the two front door monkeys ask for.
Trade Your Way to Talah Ramah
Remember to bring a Picnic Lunch, a Skip Sandwich, and the Pencil Eraser. If you do things correctly, you won't have to leave the cave to get any of the things that the monkeys need. There is only one thing that you need to remember in order to not have to leave the cave, and that is: When you get a pizza in the cave, give it to the girl monkey first. If you give it to the boy monkey instead, you'll have to leave the cave in order to call Mach Pizza from the drug store to get a pizza for the girl monkey. Ladies first!
Other than the Pizza sequence, the cave is 100% straightforward. Some of the doors lead to rooms that just have items (but they're useful items, so don't skip them.)
Eventually you'll find a door blocked by a pencil statue. Use the Pencil Eraser to get rid of it. Go through, and in this silent room floats the monkey master, Talah Rama. Talk to him to receive his enlightened words of simian wisdom.
Receive Enlightening Wisdom and Trout Yogurt
After he's done expounding on his metaphysical mumbo-jumbo (which is actually rather insightful,) he'll mention that he has the Trout Yogurt Machine that someone had left behind, and he'll give it to you. Then he'll tell you to speak to the monkey in the room when you're ready to leave. Pick up the objects from the treasure chests here, then talk to the monkey, who will go outside and wait for you.
Be sure to go around looking for any treasures that you didn't pick up earlier. There are some really nice items in here, including a Bag of Dragonite, a Neutralizer, and a Fire Pendant.
When you're ready, bid the monkey caves a fond farewell, and go outside to Dusty Dunes Desert.