N64 Bowser's Castle

Appearance in Mario Kart 64
Bowser's Castle is a race course in Mario Kart 64 and features Thwomps that block drivers from preceding to further areas. Near the beginning of the course, there is a green Thwomp locked in a cage with yellow teeth, who will shake and laugh if the player goes near it. This laugh can also be heard by the normal Thwomps throughout the course. In further corridors there are pictures of Bowser and large stone statues that shoot flames from their mouths, but they are harmless. At the end of the track racers will race on the roof of the castle. On the last lap, or when the player gets too close to the Bowser statue at the start of the track, Bowser's famed laugh plays. Thwomps are the main obstacle in this course. Most of them will move around the room and try to crush the racers, some are stationary, and some slide across the room.

Appearance in Mario Kart Wii
This course reappears as the last course of the Lightning Cup in Mario Kart Wii. Many changes have been made. In this version, lava columns spring out from the pits to cause the drivers to bowl over, specially when racers attempt to jump. The green Thwomp present in the Nintendo 64 version is no longer there; instead, it is replaced by a normal Thwomp that looks no different than the rest, but it will shake and make an angry expression when a player comes near, and also laugh. The creepy laugh made by the sliding Thwomps in the original version is no longer heard; instead, they make angry expressions and rumbling noises. The flame-shooting statues are still harmless. Bowser's laugh is still heard on entry on the final lap, or when the player gets too close to the Bowser statue at the start of the track. It is the longest track, taking around one minute per lap, and one of the most difficult tracks in the game. The bridge that comes before the long circular turn before the end is now broken.

Tournaments
In Mario Kart Wii, a tournament occurred on this track, which had players race against Dry Bowser, who utilized the ability to attack with fireballs. This tournament took place as the second tournament for March 2009, and it was restricted to karts. It was later repeated as the second tournament of June 2010, but without any restrictions. It was repeated for the third time as March 2011's second tournament, and the karts only restriction returned.

Official descriptions
Mario Kart 64
 * Manual: "Surprisingly, the Bowser's Castle has been transformed into a race ground! Because it's inside the building, most of the corners are tricky right angles. However, the most difficult part of the course is where the Thwomps are. They will block your path, and if you run into one, you will spin out. Should you be stepped by one, you'll find yourself squished flat as a pancake."

Mario Kart Wii
 * Official European website: "Racing over the red carpets in Bowser's not-so-humble abode might make you think you're in for a warm welcome from the king of the Koopas. Well, if fire-breathing statues are your idea of a warm welcome..."

Trivia

 * The Thwomps' laugh in the N64 version is the same as Wario's only pitched down. Because Wario's voice changed for the international release the Thwomps' voices changed with it.
 * In the N64 version, the Bowser statue at the start of the course has eyes that will light up while Bowser's laugh is playing. Kenny James replaces the voice of him in Mario Kart Wii using the updated voice of Bowser.
 * The Bowser portraits in the N64 version use his artwork from Super Mario Bros. 3 which was also used in the sliding puzzle in the Lethal Lava Land level in Super Mario 64. The Wii version portraits resemble his artwork from Super Mario Galaxy.
 * This course makes Mario Kart 64 one of the three Mario Kart games where there is only one Bowser's Castle race course (the other two being Mario Kart: Double Dash and Mario Kart 8. Mario Kart 64 itself is also the only of those three games, where its sole Bowser's Castle course was in the Star Cup rather than the Special Cup.
 * The green Thwomp in the N64 version has been nicknamed Marty by fans. Several rumors about using a complicated method to unlock him were created, but no one knows where the rumor exactly came from.