From the Super Mario Wiki
Sunshine Seaside, otherwise known as World 5-1, is the first course in World 5 from Super Mario 3D World. The level is unlocked by either clearing Lava Rock Lair in World 4, or entering the secret Warp Pipe in Piranha Creeper Creek.
The first and main area of this level is a sandy beach. Here, players find palm trees, sand statues and five Key Coins. There are also Koopa Troopas and a team of Chargin' Chucks. The so-called "sea" ends at a bottomless pit.
The Key Coins open the Warp Box to the next area, a floating island with the Checkpoint Flag and a Warp Pipe. Players are sent to a cavern where they ride Plessie through a river, dealing with Splounders and moving bridges along the way. Another Warp Pipe at the end of the cave takes the players to the final island, where the Goal Pole and some Para-Biddybuds are found.
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