Bowser Castle 4 is a race track in the game Mario Kart: Super Circuit in the unlockable Special Cup. It is the third race in the Special Cup, and the first of its kind to appear at the penultimate spot of the Grand Prix, before Rainbow Road. It is the longest course in the game. 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.
Initially, there is a left-right turn followed by two normal left turns, after which there is 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.
This is the only GBA Bowser Castle course that has yet to become a retro course in the later Mario Kart games.