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 is another Bowser waiting for them 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 the game's final boss, Wart, who had captured it from the King of Subcon. 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 king'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. After beating the Koopalings at the end of each airship, Mario fall into to the castle, wand in hand, where the king has been turned back to normal.

Super Mario World
In Super Mario World, castles will be found at the end of each world, as they are in the past titles minus Super Mario Bros. 2. However, more like in Super Mario Bros. 3, one of the seven Koopalings will be guarding the castle. Yoshi cannot enter castles, as shown in the cutscene at the beginning of each castle; this forces Mario or Luigi to head to the boss without him. The technical reason of why this happens is that Yoshi is not compatible with some enemies inside the Castles, notably Podoboos.

After Mario has defeated one of the Seven Koopalings, he will save one Baby Yoshi. After the cutscene, Mario proceeds to the next world, giving the chance to save the game. However, the castles and fortresses cannot be revisited like Super Mario Bros. 3, unless the player holds both the "L" and "R" buttons at the same time while on the castle on the world map.

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 several 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.

The beginning of the game also features Peach's castle. Mario and Peach are walking through the Mushroom Kingdom when a lightning cloud strikes the castle. Mario heads off to investigate, but while he does, Peach is unfortunately kidnapped by Bowser Junior.

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 fight with Kamek and the two-part final fight and chase against Bowser in the last castle of the game, Bowser's Castle. The castle's music in the game is a remix of the one from Super Mario World.

Super Mario 3D Land
Castles also appear in Super Mario 3D Land. In the main eight worlds, four castles appear: once in World 1, once in World 5, and twice in World 8. The first two castles in the game are home to two False Bowsers. However, the two in World 8 are both Bowser's castles, and are obviously inhabited by Bowser himself. In the Special Worlds, castles appear more prominently; however, they are almost always time trials, giving the player 30 seconds to complete. Dry Bowser resides inside the Special 1, Special 5, and Special 8 castles. All the castles (including Special 8-3) has a giant Flagpole at the end.

New Super Mario Bros. 2
Castles, along with Towers, return in New Super Mario Bros. 2, acting much like it did in the prequels. The Koopalings appear as the bosses only in the Castles, as the Fortressses are occupied by Reznor. A hidden block containing a Super Leaf can be found at the end of every castle before a Koopaling battle, with the exception of Lemmy Koopa's Castle, which has a Fire Flower in a hidden block at the end.

New Super Mario Bros. U
Castles, and Towers return yet again in New Super Mario Bros. U, acting much like it did in the previous New Super Mario Bros. titles. However, the path to the bosses are different. Mario and co. have to now shoot themselves out of a cannon to reach the airships the Koopalings reside in.

Super Mario 3D World
Castles are confirmed to appear in Super Mario 3D World, similar to Super Mario 3D Land and the New Super Mario Bros. games.

Mario Kart series
Several of the racecourses in the Mario Kart series have had castles, either as part of the course or as part of the background. The most prominent castle in the sub-series is Bowser's Castle, as it appears as one of the courses in every game in the series.

Peach's Castle has also had some appearances in the series. The Royal Raceway track of Mario Kart 64 features the castle, but in the background. In Mario Kart: Super Circuit ' s Rainbow Road, the castle can be spotted on top of Bowser's Castle, like in Paper Mario, in the background. In Mario Kart: Double Dash!!, it appears on Mario Circuit and vaguely on Mushroom Bridge, but also as part of the track's background. The back of Peach's Castle is featured in Mario Kart DS, on the Peach Gardens course. In Mario Kart Wii, the castle once again appears in the background of Mario Circuit. Mario Kart 7 also features Peach's Castle (once again on Mario Circuit), although this time it is a part of the track and the player is able to drive up a windy path inside of the castle.

Super Mario World 2: Yoshi's Island / Yoshi's Island: Super Mario Advance 3
Like in most 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.
 * Every castle in the New Super Mario Bros. series has a Hidden Block next to the boss door, containing a power-up.
 * In the Pikmin Adventure attraction of Nintendo Land, stage 14 "Out of the Darkness" features a structure at the start that resembles to the Castles in Super Mario Bros.