In Genesis, Noah was told to make a door on the side of the ark. Genesis 6:16 describes the ark's layout and specifies one door, along with a lower, second, and third deck.
The door is part of a short set of construction instructions given before the Flood. The passage also mentions a window or opening, but it distinguishes that feature from the door. After Noah and the animals enter, Genesis 7:16 says that the LORD shut Noah in, a detail that gives the doorway a major narrative role.
Translations vary in how they render some architectural terms, and the biblical text does not provide a modern blueprint. It nevertheless clearly names a door and three levels. Paintings and films often show large hinged doors, loading ramps, or multiple entrances, but those visual choices should not be confused with the specific wording of Genesis. The account identifies the door's location as the side of the ark.