Castle

Castles are the most common work places of the Bosses in the Mushroom World. Small castles can be denominated. Castles can be characterized as being the home of some main bosses like Bowser. Although in most games Castles look pretty much the same, they tend to change from game to game.

Super Mario Bros.
In Super Mario Bros., Castles are made of red bricks, and all of them have the same basic shape. The castles can be found at the end of each world, and inside the Player will encounter Bowser, which turns out to be a fake, as there's another Bowser waiting for him in the next castle. This will go on until Mario reaches World 8's castle, where he will find the real Bowser, and Princess Toadstool.

Super Mario Bros.: The Lost Levels
As Super Mario Bros.: The Lost Levels is almost identical to Super Mario Bros., Castles play the exact same role in this game, and look almost exactly the same too. There are two castle levels where Bowser resides.

Super Mario Bros. 2
In Super Mario Bros. 2, there is only one real Castle. It is located in the clouds, and is inhabited by Wart, the game's final boss. However, the Subcon King originally resided in this castle. This castle is unique among most castles in the Mario Series, looking like a huge grand palace, instead of a battered fortress for the Boss.

Super Mario Bros. 3
Castles in ''Super Mario Bros. 3" are found at the end of every World, but will not actually be inhabited by a boss battle (except for World 8 which has Bowser as the boss), instead there will be the King of the World Mario is in, who has been transformed into an animal by one of the Koopalings who stole the Kingdom's Magic wand. After getting to the castles in this game, Mario will board one of the Koopalings' Airships, where they will find the boss of the world.

Super Mario World
In Super Mario World, castles will be found at the end of each world, as they are in Super Mario Bros.. However, more like in Super Mario Bros. 3, one of the seven Koopalings will be guarding the Castle. Also, Yoshi cannot enter castles, so Mario or Luigi will have to go in without him.

Super Mario 64/Super Mario 64 DS
In Super Mario 64 and Super Mario 64 DS, the main hub world is Princess Peach's Castle. Princess Peach's castle is the living place of Princess Peach and some other Toads, as well as Toadsworth.

New Super Mario Bros.
In New Super Mario Bros., Castles work the same way they do in the original. The player does not fight a False Bowsers, but faces other bosses, like Petey Piranha. They are filled with traps, and each are unique to each other. The last castle in the game is Bowser's Castle.

New Super Mario Bros. Wii
In New Super Mario Bros. Wii, there are castles for the player to enter and they work the same way as they do in the prequel. At the end of the castle is a boss fight against the one of the Koopalings and the two-part final fight and chase against Bowser in the last castle of the game, Bowser's Castle.

Mario Kart series
All the games of Mario Kart Series have had castle racetracks. Most of the Castle racetracks are based on Bowser's Castle, but some are a few are around Peach's Castle instead. A screenshot from Mario Kart 7 showed a track that drove through Peach's Castle.

Super Mario World 2: Yoshi's Island
Like in Super Mario World, and most of the other games, the castles in this game are found at the end of the World the Player is in. However, the creature found at the end usually does not intend to harm Baby Mario and Yoshi, until Kamek comes, and transforms it into a huge boss for the Player to fight, trying to slow down or even stop Yoshi from reaching Baby Bowser's Castle. Once the player gets to Baby Bowser's castle, even though it is guarded by Kamek, the player does not get to fight Kamek; instead, the player will fight Baby Bowser, powered up with Kamek's magic.

Super Mario RPG: Legend of the Seven Stars
In Super Mario RPG: The Legend of the Seven Stars, near the beginning of the game, Mario will go to Bowser's Keep to rescue Princess Peach from Bowser. Also, castle-like areas appear in some places.

Paper Mario series
A castle of some form appears in the end of almost all the chapters of Paper Mario and its sequels.

Trivia

 * In the 2010 version of Nintendo Monopoly, there is a Brick Block card that rewards the player with $100 for inheriting a castle.