The Great Sea

The Great Sea is a purple streamer area seen in Paper Mario: The Origami King. It acts as a hub, connecting the 11 islands in the area and the Princess Peach. It can be accessed once Olivia is trapped underneath the boulder at Sweetpaper Valley, but isn't fully explored until after the yellow streamer area is cleared. There are no hidden Toads or Not-Bottomless Holes here.

Layout
The Great Sea is a large, ocean-like area connecting several islands. It is navigated using Sea Captain Toad's boat. When first accessed, a thick, impassable fog covers most of the sea, concealing everything but Scuffle Island and the Princess Peach. After completing Bonehead Island's puzzles, the fog clears, making all of the islands accessible. Several enemies are seen roaming around the ocean, and will fight Mario if the ship gets too close.

The Great Sea is first used to reach the Princess Peach and get Bob-omb's spare fuse. It is again used after rescuing Captain T. Ode and getting his Sea Chart, which allows travel through the fog to Bonehead Island. All purple streamer events then happen here. The streamer is shown cutting through the sea floor at multiple points, but eventually leads to the top of the Sea Tower.

Several Toads on islands in the Great Sea will tell the location of treasure chests on the sea floor. This requires the Super Marino to go to the spot on the map, dive to the ocean floor, and search for and grab the treasure.

Islands
The Great Sea also contains the cruise liner the Princess Peach.

Trivia

 * The Great Sea is largely based on the overworld of the same name in The Legend of Zelda: The Wind Waker, sharing the same English and Japanese names as well as many similar mechanics, which the place itself also appeared in the Pirate Ship stage in the Super Smash Bros. series.