The Legend of Zelda The Wind Waker 100% #33 MJU's Oasis (No Commentary)

Look for a flock of seagulls on your way to this island. Just skim the horizon with your Telescope or go to the oasis island and get a hint as to the location by old man Ho Ho (the guy with the telescope). Sail close to the seagulls and a Big Octo will appear. Using your Boomerang (or arrows or bombs), take out the giant squid monster's eyes next until it croaks. Look for a sparkly spot where it sank and use your grappling hook to retrieve a treasure chest with an Orange Rupee (100).

Sail to the oasis island and start to explore. For starters, you can crawl underneath the house and collect some Rupees.
Next, climb the fence as shown above and hop across to the plateau (with the help of your Deku Leaf). You can also use your Hookshot, if you've got it. You will find a treasure chest with Treasure Chart 27. There are a few hidden rupees in the waterfall, as well. Simply fire your Hookshot at it from the bottom level.

To do anything else on this island, you have to prove that you're the rightful owner of the cabana. To do this, you need to first get the Cabana Deed from the school teacher on Windfall Island. Refer to the Windfall section here on how to do this. Walk up to the door of your house and show the Deed while standing in front of the door (the Cabana Deed is in your Delivery Bag).
The door will be unlocked. Inside your new home, you can play slide puzzles to your heart's content and make some Rupees (not to mention break the sparkly pots with your Grappling Hook for some extra cash) -- but there's of course more to this house. Look up.
Shoot your Grappling Hook at the bar hanging from the ceiling to turn off the fire in the fireplace. Enter the fireplace and drop through the hole.
In The sewer I Used the Speedrun Route To do it. Stand on the wind tile and play the Wind's Requiem. Open the chest that appears to get Triforce Chart 2 Exit the sewers.