The Big Bridge

The Big Bridge is a place located in the south part of the Music Box World in Wario Land 3. When Wario goes to the south part for the first time, the bridge isn't down. But by using the first Music Box found in The Grasslands, it is accessible.

The level itself is a long gray bridge. Wario has to cross it to get some treasure. Upon stepping on it, flying fishes will try to stalk Wario and send him to the entrance.

There are also some doors underwater that the player can access.

Grey Chest : Miracle Seed
To get this treasure, Wario has to get the key which is located on the entrance's left. Then, he has to cross the bridge by avoiding a series of flying fishes. The treasure chest is just across the bridge.

The Miracle Seed will make vines grow in The Pool of Rain,The Grasslands and The Vast Plain. It allows Wario to open new paths.

Red Chest : Cyan Crayon
Wario needs to get the second power-up found in Tower of Revival to gain access to this treasure. To get to the chest,he only has to enter the door located deep underwater and avoid the Brr Bears to get the red key and open the red chest.

This crayon colors the sky of the hill that separates the north side from the south side.

Green Chest : Pokémon Pikachu
To get the treasure, Wario needs to pick up the red barrel located in the left side of the entrance. Then use it to break the blocks at the right side of the level. The green key is in a room that Wario can enter using an underwater door.

As for the chest, it is located by entering the door accessible after breaking the blocks with the barrel. Wario has to play a minigame of Golf and rise the minigame block which leads to the chest.

The treasure serves for no purpose.

Blue Chest : Lanturn of Truth
To get this treasure, Wario needs the Spiked helmet. First, he must enter the door located in the left side of the level and search for the blue key. When found, he has to go underwater and break a serie of blocks using his helmet(and his Bubble Form). When done so, he has to climb the ladder located in the right side of the underwater area. Now that the blocks are broken, he can access the treasure chest.

The Lanturn of Truth, along with the Flammes of Truth make the Castle of Illusion appear on the east side.

Trivia

 * The Grey Chest's treasure, the Miracle Seed, has the same name as an item in Pokémon games that is used to power up Grass-type moves.