Wario Castle (or Wario's Castle) is the castle that serves as the home of Wario in several games. It makes its formal debut in Wario Land II, where Captain Syrup seeks her revenge and has her pirates sneak into it, stealing massive amounts of treasure from Wario early in the morning. Wario spends the game in search of his treasure and the crooked captain, which he eventually recovers.
In Wario World, Wario has recently completed the construction of his castle, now decorated with the gold and jewelry. His happiness with his wealth is short-lived when a mysterious treasure that he stole named the black jewel awakens. It destroys Wario Castle and turns it into its own world in its own dimension, all connected through Treasure Square. To get his castle and possessions back, Wario travels through the four worlds the jewel created, which includes Excitement Central, Spooktastic World, Thrillsville, and Sparkle Land. Wario eventually defeats the black jewel and rebuilds his castle, but its quality is determined by the number of Spritelings that are saved by the player on the adventure.
In later titles, the castle has appeared more scarcely, although Wario Palace from Mario Superstar Baseball is a similar location. Wario is instead shown spending time in his smaller home, although he was originally shown to have a larger one. After a lengthy absence, the castle appears on the Wario Board in Mario Party 10, a Wario-themed board filled with references to both the Wario Land and WarioWare series.
Prior to the proper introduction of Wario Castle, Mario's own castle was taken by Wario when Mario was away. During the events of Super Mario Land 2: 6 Golden Coins, Wario cast an evil spell over Mario Land, brainwashing its inhabitants into becoming his mindless followers and ultimately transforming it into his own palace. By the end of the adventure, Wario fled and relinquished ownership of the castle to Mario.
After losing the castle to Mario, Wario was more determined than ever to have a castle in Wario Land: Super Mario Land 3. He comes to Kitchen Island to seek the stolen golden statue of Princess Toadstool, which he plans to return for reward money. However, Mario ends up swooping in and claiming the statue when it is revealed under Syrup Castle. The ending of the game wherein Genie grants Wario's wish depends on the amount of money the player earns in the game. Collecting a certain amount of treasures grants Wario what is presumed to be Wario Castle, but other outcomes include the smallest home which is a bird house, or the largest possible home which is an entire planetoid with Wario's face on the surface (the player is urged to try again if this is not the result).
In the SNES version of Wario's Woods, another version of the castle makes a brief appearance in the heart of the woods. It is first seen as the final level of VS Com as it is the setting in where Toad, the game's protagonist must fight the other bosses, including Wario himself. The castle also makes an appearance at the end of Round Game. As Wario rages on by plane, Toad throws one final bomb at his castle. The explosion of the bomb causes the castle as well as Wario and his plane to go crashing down in defeat. Unlike the NES version (which has a different ending), it is discovered that Wario's Woods has returned to peace, implying that the castle's construction was the source of the corruption of the forest.
As noted above, depending on the amount of spritelings saved, other versions of Wario Castle were seen in the various endings of Wario World depending on how many spritelings Wario saved by the end of the game. In particular: