Bowser's Castle 1 is a level in A Koopa's Revenge that Koopa must pass. It is the first level of Bowser's Castle and the first level overall. It serves as an introductory level of the game. It is proceeded by Bowser's Castle 2.
Koopa starts out through a passage that leads him into a pool of lava. He encounters a Baby Mario and a Toad. There is a door that leads to the next room. A secret door with a Fire Flower and a Bowser Coin is found behind where Koopa started that serves as a shortcut.
In the next room, Koopa jumps over a flying Birdie and encounters a Yoshi. He reaches a place where many bricks and blocks are found. Koopa jumps over some pools of lava and reaches a door down below.
Here, Koopa enounters more obstacles and encounters many Yoshis. Baby Luigi is also found here. There is a Bowser coin that is floating high above near the door to the next room.
More obstacles and enemies are found in the next room. Koopa has made it to the Flagpole checkpoint. It starts to get even dangerous because of the Thwomps and the Fire Balls. After those, Koopa jumps to the door up high.
Koopa discovers invisible blocks that help him reach the other side of the lava. Baby Wario is found in this room and Koopa finds two doors - one that he needs to jump across the lava and another that he just needs to jump to. An unreachable Bowser coin is also found here.
If Koopa took the higher door, he would be able to get Baby Waluigi. Koopa then makes his way through an obstacle filled with Fire Balls and reaches the next door.
After going through a few more obstacles, Koopa finally makes it thorugh the level and reaches the Large Flagpole. Koopa is now on his way to Bowser's Castle 2.