Donut Secret 1 is a level to lead a secret. It is an underwater level, and the first secret level. It also first introduces Rip Van Fishes and Blurps. Its secret leads to a Ghost House, as its boss is the Big Boo. The key is under blocks.
This underwater level consists of one long underwater screen and an above ground room. The player has 300 seconds on the Timer to complete the level.
The underwater screen has many Rip Van Fish, Cheep Cheeps, and Blurps, while the underground area has Koopa Paratroopas. To get into the area, the player must enter the first blue Pipe. Right before the Pipe are ? Blocks, and above them is the first Dragon Coin. There are two ? Blocks in the area which contain Power Balloons. There is another ? Block that contains a Super Mushroom or a Fire Flower. The player must use the Power Balloons to float up, and if either top corners of the room are reached, the player finds a Dragon Coin. Next to the exit Pipe from the underground area, there is another Dragon Coin. In the Game Boy Advance remake, there is a Midway Gate after the Pipe and near the Switch Block. Around that same area is a Dragon Coin, in between two Grab Blocks. To the left of the Keyhole is another Dragon Coin. The last Dragon Coin can be found before the Giant Gate, hidden above a wall. The Giant Gate can be found on the right edge of the screen, a little ways past the Keyhole.
The secret exit can be difficult to find, as the key requires strategic use of the Switch Block. To find the key, the player needs to carry the Switch Block to the row of Empty Blocks, and then stomp on it. This changes some Empty Blocks into coins, giving access to a ? Block. Before the Switch Block time runs out, the player has to collect some of the coins and hit the ? block for the Key to pop out. The Keyhole is just right of the key.