The Forbidden Archives are 3 library like buildings located in the Simulation, inside the Subterranean Lake area. Accessing them is crucial for finishing the Echoes of the Eye DLC.
Shrouded Woodlands[]
The Shrouded Woodlands archive is located behind a fireplace in the large communal building at the darkest part of the forest. To reach it you must either run through the building which usually has many Pursuers, or wait until the dam breaks and reach it using the simulation rafts. This archive has a bug report on how you can jump off the rafts when going between different simulation areas, and an unburnt Ringed Planet slide, depicting how they destroyed their home planet to build the Stranger.
Starlit Cove[]
The Forbidden Archive in the Starlit Cove is accessed by going to the large well in the middle of the area. It is guarded by a Stone Sentry however, making it impossible to reach unless you are dead in reality, or turn off the candles surrounding the well. Inside the well you will reach a theatre with a Pursuer guarding the path. Avoiding them, you will reach another stone sentry which can easily be avoided, before finally reaching the Archive. Inside there are 3 accessible reels, showing how the Strangers discovered that dying is the same as sleeping and will get you into the simulation, a bug report showing a dead Stranger avoiding a Stone Sentry (i.e. the Stranger does not wake up because its body is dead), and the last one being an unburnt Eye of the Universe Reel, revealing how they built the probe to block the Eye's signal.
Endless Canyon[]
The Endless Canyon archive is accessed through a painting which must be in the dark to open. To achieve this you must cross an invisible bridge, and extinguish a totem. Then you must avoid Pursuers, light a totem in the Mess Hall to activate a bridge (or make use of a second invisible bridge to circumvent the Pursuers), and avoid another Pursuer to reach the archive. In it there is a bug report on how you can walk away from your Artifact to leave its projection radius, and an unburnt Artifact slide reel, revealing that the dreamworld is in fact a Simulation.