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 as early as after Bob-omb rejoins Mario and Olivia in Chestnut Valley (after which an engine for a boat docked at Toad Town is ready, provided that Mario has rescued the Sea Captain Toad in Autumn Mountain by that point), but is not fully explored until after the yellow streamer area is cleared. Additionally, Mario and Bob-omb are required to set sail to the Great Sea after Olivia is trapped underneath the boulder at Sweetpaper Valley. There are no hidden Toads, ? Blocks, or Not-Bottomless Holes in the Great Sea itself; however, there are numerous treasures to be found in its depths.

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 the puzzles at Bonehead Island, the fog clears, allowing access to all the other islands. Several enemies are seen roaming around the ocean, and will fight Mario if the boat gets too close.

The Great Sea is first used essentially to reach the Princess Peach and get a spare fuse for Bob-omb. It is again used after rescuing Captain T. Ode and getting his Sea Chart, which allows the party to travel through the fog to Bonehead Island. The purple 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 mark spots on the Sea Chart to dive for treasures as thanks for Mario rescuing them. The Super Marino is required to dive at those spots to search for and grab the treasures. Additional items that can be collected from the sea floor include a Heavy Bag, a Canned Heart, a Big Shell, and some coins.

Islands
Mario can access a total of 11 islands in the Great Sea. Each island, with an exception of the Sea Tower, has a stone Toad statue that Mario can examine. If Mario finds all Toad statues across the Great Sea, he is rewarded a Collectible Treasure of a Shangri-Spa Toad Statue (No. 80).

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.