In the early books it was filled with traps, projectile firing devices, flamethrowers, and mechanical dangers such as presses, collapsing walls and the like intended to challenge the trainee. Meanwhile, an observer is in the overhanging control booth managing the room's mechanisms to oversee the exercise while manually ensuring the subject's safety. Later the Danger Room was upgraded with machines and robots for the X-Men to fight against.
After befriending the Shi'ar the X-Men rebuilt the Danger Room with Shi'ar hard-light holographic technology. These upgrades were largely added by Dr. Hank McCoy. The Danger Room is located in the X-Mansion; every destruction of the latter led to a rebuilding, and usually upgrading, of the Danger Room. The training facility has endured a lot of damage over the years, usually from X-Men training or X-Men going rogue, as Colossus did during The Muir Island Saga. Supervillains have dealt critical damage to it as well as taking over the facility, especially Arcade. The security and safety protocols that ensure the safety of anyone using the Danger Room have frequently been disrupted, tampered with by villains, failed, or have been completely negated in all the years of its use, each time happening more frequently as the room began to get more and more upgraded.
It is suggested in the X-Men Official Guide that the objects in the danger room are holograms surrounded by force fields, supposedly confirmed in Astonishing X-Men when a student managed to kill himself by jumping from a holographic cliff face. It is also revealed that the Danger Room can display holograms in only 32-bit color.
The Danger Room has played an important role in the everyday lives of the X-Men since the beginning. It provides a central and controlled location for training where the X-Men can learn to control and develop their abilities in normal and combat-like situations. The original Danger Room employed many mechanical weapons and dangers including flying projectiles similar to missiles, obstacle courses, trap-floors, fire, crushing walls, and much more. The layout of the Danger Room has not changed considerably since its earliest mention. The room itself is quite large, and there is a central control room and observatory overlooking it where the entire room can be controlled by a single person. Since the beginning the Danger Room has underwent a series of upgrades. The first was the addition of robots to the room for combat training. Later, Shi'ar technology was incorporated by Beast, upgrading the room to incorporate realistic holograms to the training and adding to the weapons and traps that the X-Men faced while training. At some point the Danger Room has gained sentience. It is unclear when this happened, but it was revealed that Professor Xavier was aware it and chose to leave it imprisoned in the room. The room began to attack students that were inside, and its core was accidentally freed by Wolverine. Constructing a body resembling a human female, Danger has become an enemy of the X-Men. Currently the Danger Room is inactive as it has lost its control system.
The Danger Cave was first introduced in New X-Men #21. It was built by Prodigy, using skills he obtained by being around Hank McCoy and Kitty Pryde. This was originally built with the intention of being used as an additional training device for his New X-Men teammates. However, after M-Day drastically decreased the amount of students attending the school, the cave was rarely used. In the few instances the Danger Cave was utilized in New X-Men, the New X-Men and the Hellions relived some classic X-Men battles. The classic battles depicted by the Danger Cave consisted of Fall of the Mutants, X-Men vs. the Brood, a battle with a Nimrod, and Inferno. The Danger Cave also made an appearance as a base of operations in the first arc of Young X-Men, Final Genesis. The cave was shown to be large enough to house a couple of jets that the team used to confront some of the New Mutants. The Cave was also shown to have a cell that was used to briefly imprison Magma. The most notable use of the Danger Cave's holographic cabalities came after Magma heated the sand that Dust is composed of, turning her to glass. The Young X-Men attempted to use the A.I. versions of Beast, Nightcrawler, Reed Richards, and Moira MacTaggert to cure Dust's condition, however the A.I. just couldn't come up with a viable solution.
The Danger room is a spherical room that can produce holographic images that feel, smell, sound, and most likley can even taste like real things.
- Viewing Deck: The Danger Room has a circular viewing deck attached to the ceiling, which also holds all the controls that power the room.
- The appointing of the name "Danger Room" was first used by Xavier in Uncanny X-Men 2 after which the narrator descibes it as "a huge unfurnished chamber which houses countless hidden perils!"
- The Danger Room was shown at the beginning of X-Men: The Last Stand. It was being used to train the students Iceman, Shadowcat, Rogue, and Colossus. Wolverine and Storm were advising the training session. Also it appears like it's Days of Future Past the Danger Room is using to train the students. The thing that is chasing them looks like a Sentinel.