This switch can be hit with the slingshot, boomerang, bomb, and bombchu. It can also be hit with the sword or a deku stick with a difficult hover off the nuts of the Octoroks.
This is the biggest sequence break for this dungeon. With it you can skip everything between getting the Boomerang and the last room before the boss. It skips killing the tentacles, Big Octo, and a few other rooms. There are two parts: getting over the gap in the room with the raising platform and getting through the door.
Skipping Bigocto requires you to get over a large gap in the raising platform room. There are multiple methods for crossing it, but these are the most useful.
A well angled megaflip from the left ledge will make it
Recently, there has been increasing use of a megaflip using one of the boxes in the elevator room. It can be seen here.
A more difficult megaflip from a Biri can also make it over the gap. The area where you can start the megaflip from and still make it is small, and requires you to be as close to the ledge as possible. By luring the Biri, you can give yourself enough time to set up for a megaflip from it. Having ISG greatly helps position yourself near the ledge.
Using the Biri, you can hover up to the ledge after the miniboss, and then lower the platform like normal.
The first method found. You need a bottle with a bug or fish to do this trick. Using ocarina items allows you to keep the item in the bottle.
Ocarina items method:
Bottle switch trick:
This was the second method found, and significantly harder than the bottle switch trick. However, it can be done without a bottle, so it was used commonly until Method 3 was discovered.
This was the latest method found, and the fastest, and best of all, it only requires a sword.
Line up against the wall beneath the switch and pull out a bombchu. Release it on the 5th flash and it should activate the switch.
Pull out the boomerang and aim as high as possible, and just a little left of the web. As soon as you release it, start sidehopping and when it starts coming back it should hit the switch.
It is possible to megasidehop into the loading zone as an adult. This is extremely difficult.