You start in the sand at the start line. Once the race starts you will drive over a yellow Lego bridge with item boxes into the Lego castle. Once inside you can go on five paths. Three of them are long, flat, colored building blocks that lead to the second floor while the two paths between those three blocks let you continue on the first floor. The lower paths also have speed bars and will lead into a water section. In the middle of the section is an underwater tower where you can drive through and grab an item box. However on the sides of the tower are also item boxes. If you decide to go the the second floor you can drive on one of the two ladder bridges, but can drive into the water anytime you want. On the middle of the bridge are item boxes, the tower also extends out of the water.
The underwater path and the bridges come together again and you will enter a red slide that goes downwards. It first makes an U-turn and near the end of the slide are item boxes to grab. You then land in the giant sandbox and can go two way. One way is driving forwards, get the speeding bar and single item box underneath the robot or take the side, which is higher sand, and get multiple speeding bars. And then you arrive at the finish.
The castle itself is a big yellow castle made out of giant Lego bricks. Like Bowser's Castle always has his head above the gate, Junior's Playhouse also has a Lego version of Bowser Jr.'s head above the gate, between the two towers. The walls of the first chamber are still from Lego, but the floor is just canvas. One the left side is the bottom of the Koopa Clown Car. The wooden planks are colored red, blue and yellow. When you enter the water it is similar to how you enter the water in the Twisted Mansion stage. The off-road in the water are those little colored stones. The water also has a treasure chest, colored seaweed a sunken toy boat. On the bridges you are able to spot a rubber duck floating on the surface. On top of the tower are Koopa's. When you go down the red slide you will see many toys. In the U-Turn is a kids version of a Tower of Hanoi. On the outside are letter-blocks stacked on each other. There also is a wooden plank on top of two block towers where you drive under. In the sandbox is a big robot you can drive underneath.