The Maw

The Maw is the setting of both Little Nightmares and the DLC Secrets of the Maw.

Summary
The Maw is a large, mostly underwater, floating, mobile island location that Six, The Runaway Kid and the other children are taken to. This is where the entire game takes place, and the player must navigate the many rooms in order to escape it and its inhabitants.

The Maw is made primarily of metal, with many electrical-powered devices, vents, drains and hiding places. Periodically, it can be seen that the entire place is floating, as the rooms sway back and forth and objects roll freely with the swaying. There are many rooms in the Maw, but much of it is in disrepair. There are areas dedicated to housing prisoners, to food processing and to accommodating The Guests and The Lady, as well as a great furnace powering machinery in the depths of the Maw.

The Prison
The Prison is the first location of Little Nightmares, where Six begins. There are lots of different kinds of rooms - from nurseries with other children, to prisons full of cages. Various kinds of furniture, luggage and random items abound. The only harmful creatures here are the Leeches, although Six can see The Janitor at one point in the distance. There are numerous hazards, including electrified bars, sliding platforms and a beam of light that can turn a child to stone.

The Lair
After escaping the Prison, The Lair is the second place Six visits in the Maw, and this is where the Janitor lives and bundles child prisoners into packages to put onto hooks and send to the Kitchen. The Lair has bedrooms, bathrooms, and various store rooms, and through it all, Six must avoid the predations of the blind, but long-armed Janitor (as well as a mysterious creature living in a pit full of shoes). Eventually defeating the Janitor will lead Six to the Kitchen.

The Kitchen
The Kitchen is the third location explored by Six in Little Nightmares. It appears disorganized, uncleanly, multi-leveled, and is run and occupied by the Twin Chefs, who are seen viciously preparing meals for the arriving guests. This area also includes a dish washing area, the Twin Chefs' room, and several meat lockers storing large quantities of meat (presumed to be bodies), which are later processed into sausage. After escaping the Chefs, Six is dropped off in the Guest Area.

The Guest Area
The Guest Area is the fourth location in Little Nightmares. Here, Six watches the arrival of The Guests boarding the Maw from an unknown vessel and eventually follows them into the dining halls which are designed like a Japanese cuisine restaurant, but filled with grotesque, obese guests stuffing their faces with food. Most can be bypassed without hassle, but some will notice Six and pursue her by dragging their bodies across the floor to devour her. If she can escape all of the Guests, Six will find herself in The Lady's Quarters.

The Lady's Quarters
The Lady's Quarters is the fifth and final location in Little Nightmares. Here, we discover The Lady seen in the "nightmare" during the start of the game. This is a short area, with just a few rooms, mostly filled with mannequins dressed similarly to The Lady. After defeating The Lady, Six consumes her (and her powers) and slowly walks back through the Guest Area, apparently absorbing the essence of any Guest that gets too close to her. Finally, she finds herself on the Outside of The Maw.

The Depths
The Depths are the first unique location found in the DLC. Composed primarily of flooded rooms in the depths of The Maw, this is the first area The Runaway Kid lands in after escaping the Prison area. This is the home of the grotesque aquatic creature, The Granny. After defeating her, The Kid moves on to The Furnace.

The Furnace
The Furnace is largely filled with Nomes and coal and machinery, and the Kid must find a way to recruit the Nomes to help him start the great furnace to help him on his journey.

The Residence
The third part of the Secrets of the Maw DLC, this place shows more of the Lady’s home - mostly her library and sitting rooms. And reveals secrets about many of the characters in the game.

Official Summary
"The Maw arrives every year. Always at the same time, but never in the same place, it creeps and crawls and buries its claws deep beneath the glistening water. And there it sits in vast silence. Waiting.

Soon after, they start to arrive. The guests. The monstrous, sweating, hungry guests. All seams bursting, bodies bulging, eyes dead with boredom. They shuffle up the gangway and into the mouth of The Maw. And then they are no more.

For none of those that enter have ever returned to tell the tale. At least, not yet..."

Trivia

 * The word "Maw" means "the mouth of a greedy and insatiable person/animal."