GBA Bowser's Castle 4

Bowser's Castle 4 (known as Bowser Castle 4 prior to Mario Kart Tour) is the third course of the Special Cup in Mario Kart: Super Circuit. It is the first Bowser's Castle course to appear as the third course of the Special Cup before Rainbow Road, a trait that would later be shared by every new Bowser's Castle course in future main-series installments. It is the longest course in the game and shares its music with the game's other three Bowser Castles: 1, 2, 3.

This course features many dangerous jumps over lava pits, several Thwomps blocking the way, and Mechakoopas at the end of the race. What appears to be a large generator with Bowser's emblem on it can be seen in the background. Unlike most stages with Thwomps, some of the Thwomps on this stage are capable of moving horizontally, moving further down the track and back at regular intervals before slamming down.

This course makes its classic course debut in Mario Kart Tour as part of the 2023 Bowser Tour.

Mario Kart: Super Circuit
Initially, there is a left-right turn followed by two normal left turns, after which there is a long, wide stretch of ground littered with square pools of lava that let out Lava Bubbles. This ends with a left turn, three right turns (with Thwomps near the last) and a left turn that leads into a thinner pathway. After another right turn the player is given the choice to take the right, narrow and (due to the boost panels) speedier route forwards or the left, wide and slower route forwards. Afterwards there are two more right turns, another split path filled with jumps, followed by a larger jump over an earlier portion of the track. The subsequent right-left turn has several Mechakoopas before the upcoming left turn. There is another left turn, two right turns and a final U-turn (with two Thwomps right in the middle of it) before the finish line is reached. Overall there are eight (a group of three, two, a lone one and another pair) item boxes on this course.

Mario Kart Tour
Bowser's Castle 4 makes its classic course debut in Mario Kart Tour, starting with the 2023 Bowser Tour, making this the first Special Cup course from Mario Kart: Super Circuit to return in another Mario Kart game. Twenty-two years elapsed before this course received its first reappearance, the longest time period out of any course in the series so far, beating Yoshi Desert by nearly a month. While it is still fashioned after the aesthetic of GBA Bowser's Castle 1 instead of keeping its original visuals, the castle is now depicted as ruined, and the track has been given elevation and regular road portions, bringing it more in line with other GBA course remakes in Tour. New obstacles and elements have been added, like metal balls (possibly as a nod to Big Steelies). The Mechakoopas are removed in this version. Two new gliding sections have been added, with one leading into a new split route in the bottom section of the course with pillars that can be tricked off of and a second one along the final stretch on the other route. Like the other GBA Bowser's Castle courses in the game and RMX Bowser's Castle 1, this course reuses Mario Kart 7's arrangement for GBA Bowser's Castle 1. This course is a favorite of Luigi (Golf), Toadette (Sailor), Luigi (Chef), Kitsune Luigi, and the Bowser, Castle, Spike, and Iggy Mii Racing Suits. It is also a favorite of the Ludwig Mii Racing Suit if it reaches level 8.

The course is also now a section-based course, similar to Wii Rainbow Road. Unlike that course, the sections appear to be clearly marked with other starting banners. This is the first section-based Bowser's Castle course in the series. Two parts of the road that overlap each other are depicted as connecting on the minimap.

GBA Bowser's Castle 4 is not only the first track added to Tour since the Battle Tour to not have an R/T variant upon launch, but also the first track overall to not feature a T variant at launch. It is unclear if these course variants are planned for later release or not; there are internal IDs allotted for them, but at a size of one each, no data currently exists signaling they are set to release.

For this course's tour appearances, see List of GBA Bowser's Castle 4 tour appearances in Mario Kart Tour.