The Elder Scrolls V: Skyrim/Dawnguard

Dawnguard is the first DLC for Skyrim, released worldwide for the Xbox 360 on June 26, 2012; the PC on August 2; and the PlayStation 3 on February 27, 2013. But what makes Dawnguard noteworthy is how it adds a crapload of unused data and test cells.

Test Cells
To access these, load up the console by hitting Tilde and then typing.

Area Code: DLC1NPCHome

This interior cell is modeled like a Nordic barrow. It is a single square room with two very short hallways with dead ends.

Area Code: DLC1LDUtilityCell

A Dwemer-decorated room which includes items from the DLC: the Aetherial Crown, Staff, and Shield, plus the Aetherium Crest.

Area Code: testFalmer

This interior cell is set up like a stone fortress. Behind the entrance is empty space. There are Ancestor Moths in the middle of the main room, with three locations on the ground where they can land. There is nothing of interest up the stairs. A leveled melee bandit stands next to the doorway, through which there is a small room. Embers float next to a broken part of a wall, which leads to a dirt tunnel with wooden support beams. The tunnel ends in nothingness.

Area Code: testGiant

Similar to the testFalmer cell, this too is set up like a stone fortress. In the middle of the main room is a weak test vortex with a number of items in it—four Iron Daggers, two Hide Shields, two Deathbell flowers, one Daedric Greatsword of the Inferno, and four bloody human leg bones. In one corner of the room is a test Storm Atronach (level 30), but it is disabled and does not appear. There is nothing of interest up the stairs. Through the doorway, there is a small room with floating embers next to a broken part of the wall, which leads to a dirt tunnel with wooden support beams. The tunnel ends in nothingness.

Dreamworld

 * Area Code: vampireDreamworld01
 * Area Code: vampireDreamworld02
 * Area Code: vampireDreamworld03

Three identical-looking cells that are not connected. They appear as the inside of a small house. The only door can be activated, but doesn't lead to a new cell. A few rare books and notes can be found on two shelves. Judging by the names of the location code, this was probably related to vampire quests that were not released in the final version of the DLC.