The Colossal Hole
The Colossal Hole is a level located in the east part of the Music Box World which appeared in Wario Land 3. It is only unlocked, along with The West Crater, after Wario uses the three conch artifacts to make the volcano erupt.
This is an underground level inhabited by thwomp-like enemies who turns Wario into a Flat Wario if they manage to crush him. If they do, Wario must simply get caught by a blue UFO to return normal. In the bottom of this big hole, there are Jellybobs that turn Wario into a Puffy Wario allowing him to get back to the top. A golf minigame and minigame block are found here as well.
There is an area outside the hole, reachable by using an owl. It has a Mr. Sun/Mr. Moon, Brrr Bears and a Spear-bot.
Like all the levels in the eastern part, this level is only visited nighttime. However, after Wario restores the sun emblem, he can visit it anytime. The only difference is the owls who sleeps during the day, allowing Wario to use them. At night, those owls are flying in the air and it is impossible for Wario to catch them(unless if he uses the high jump.) This is also one of many levels that has bombs in it, when Wario blows them up with The Detonator found in Beneath the Waves, new areas can be accessible.
An area full of Fire Snakes is found here as well. They're not summoned by the Flute though. Their area can only be accessible after blowing the level's bomb.
Treasuries
Gray Chest : Blue Snake Eye (right)
To get this treasure, Wario has to use his Puffy Form to get the key. He'll use the same technique for the gray chest located at the left side of the level.
After getting two of the snake's eyes, the blue snake door will open in Tower of Revival.
Red Chest: Air-Pump
To get this treasure, the player needs the Garlic Treasure. Wario first has to play a minigame of Golf, then go down the ladder at the far left of the minigame door. Then, he has to avoid the UFO enemy, break the solid blocks and enter the door at the far right.
Then, he has to take the spearhead to break the floor and get the red key. After doing that, he has to come back where the UFO enemy is and use his Puffy Form and avoid the spikes to go up. Then, he has to enter the door at the upper left which was blocked before by a minigame block. Then, he only has to break the solid blocks and open the chest.
The Air-Pump makes the ice blocks rise in The Pool of Rain and Bank of the Wild River.
Green Chest: Jumping Boots
To get this treasure, Wario must visit this level in daytime (This can be done by restoring the Sun Emblem and getting rid of the eternal darkness in the eastern part). First, Wario must use the first owl to reach the second one. Then, he has to use it and avoid the spikes to reach a door leading to an area outside the hole.
Here, Wario must run until he finds two vertically placed fire blocks. To break them, he has to turn into a Fire Wario (The Mr. Sun in this area can do that). When broken, Wario can reach the Green Key.
After getting the key, Wario must find two horizontally placed fire blocks and break them the same way he did with the other ones. Then, Wario must simply open the chest to discover his new power-up.
Blue Chest: Locomotive
To get this treasure, Wario has to blow up the bomb found in this level using the detonator from Beneath the Waves. Then, he has to use the first owl to get above the hole. The door is now accessible. Upon entering the door, Wario will find himself in an area full of Fire Snakes. He must simply use them to get the Blue Key and to get to the area where the Blue Chest is.
Getting the Locomotive doesn't effect the Music Box World in any way.
Reaction Abilities in this Level
Screenshots
Wario and an owl. 
Outside the hole. 
The Fire Snakes Area. 
The bottom of the hole.
