Room 303 is a hotel room on the third floor of the Coolest Hotel. Its windows face the Candy Drugstore. Lumpy Space Princess stays here in the episode "Candy Streets" and orders pizza from the room in order to get with Petey, the pizza delivery boy. Finn, Jake, and BMO check the room for evidence concerning the supposed theft. They find what they think is blood, but it turns out to be tomato sauce.
Lumpy Space Princess keeps the room in a state of disrepair. Dozens of pizza boxes litter the floor, bed, and nightstand, along with leaves, clothes, bottles, and leftover slices of pizza. The wallpaper is peeling, the only picture on the wall is crooked, and the bed is not made.