Natsuyasumi Island

Natsuyasumi Island is a non-canon vacation island in the New World that the Straw Hat Pirates visited to relax.

Geography
Natsuyasumi Island has a warm, tropical climate, with coastal beaches and lush vegetation. The island's central mountain is dark-colored at its peak, and while it appears to be plateaued, it was converted into a giant grill by Wadatsumi.

The island vegetation bears giant produce, including watermelons and corn larger than people.

One Piece Party
The Straw Hat Pirates traveled to Natsuyasumi Island, hoping to take a vacation and relax. They tried a range of common summer activities on the island. Luffy rode a water slide, while Sanji suggested Nami and Robin put on skimpy swimsuits. They changed into something more reasonable, and the crew's four Devil Fruit users rode on Franky's back as he jetted through the waves. After they were done swimming, Usopp prepared traps for beetle catching. He was shocked when Chopper caught Kabu, and further horrified when Luffy, Zoro, and Sanji caught his mentor Heracles.

Heracles explained that he had been visiting the island to vacation as well, and he joined in the festivities, presenting the crew with a giant watermelon to play suikawari. Sanji and Zoro fought over which of them would go first, but while they were fighting, Brook cleaved the giant fruit in half. Luffy ate half of it by himself, and while the others ate some, Sanji and Zoro continued to bicker. They decided to settle it with a beach volleyball match, one team with Sanji, Usopp, Luffy, and Chopper, and the other with Zoro, Franky, Nami, and Brook. Robin acted as the referee. The teams were evenly matched until Nami intentionally distracted Sanji, allowing Zoro to spike the ball for a winning score.

The losing team was responsible for finding food for everyone, but they encounter a ferocious giant squid, King, on their search. King sprayed them with ink, but the pirates retaliated and swiftly defeated him. Luffy asked Sanji if they could cook and eat the squid. He quickly ran up to the top of the island's mountain and called down to his friends that it was weirdly shaped. They investigated it before noticing a large round object. Luffy, Usopp, and Chopper began jumping and bouncing on it, but the round object was actually Wadatsumi's stomach. The angry fish-man punched Luffy for disturbing him, and the captain punched him back. Sanji asked Wadatsumi if he knew anything about the mountain, and the fish-man explained that he had turned it into a grill. He also had prepared nagashi-sōmen, which the pirates had earlier assumed that the flume was a waterslide. Now with a giant grill to cook their caught squid, the Straw Hat Pirates, Wadatsumi, and Kabu had a barbeque.

After the barbeque and nightfall, the crew held a kimodameshi, in which half of them navigated through the dark forest and the other half dressed up as yokai to scare them. Zoro, Nami, Usopp, and Chopper were on the Frightened Side, and Luffy, Sanji, Robin, Franky, and Brook were on the Frightening Side. As Zoro and the others walked the dark, wooded path, Sanji jumped out dressed as a Kappa, calling for Nami, but Zoro stopped him by kicking him in the face. Luffy and the others all scared Nami, Usopp, and Chopper one by one, who ran off in fear. They all reconvened but realized that Zoro was not with them, as he got lost in the forest.

Franky set up a fireworks display on the coast. Zoro had found his way inside the cannon and was sleeping on top of a giant firework shell. Franky launched them (and Zoro) into the sky, and everyone admired the fireworks as they went off. Zoro showed up looking fried from the fireworks but seemed unfazed. For their final activity, Nami and Robin made the men of the crew work on homework, as their vacation was coming to a close.

Wildlife
The only known creature on the island is a giant octopus named King. During their barbeque, the Straw Hat Pirates also cooked giant prawns, implying the coasts around the island were populated with the shellfish.

Trivia

 * "Natsuyasumi" means "summer vacation" (夏休み) when written in kanji.