Shadowlands

Shadowlands is an area in Underground Out of Bounds level, where you can see the "shadows" of level elements such as pipes and structures that are in the level on the ground, but the objects are missing.

Other Out of Bounds areas do have shadows-on-the-ground-places too, those are on every platform and do not need certain triggers to be seeable.

How and where to do it
Please feel free to use the Talk:Shadowlands page to share your experiences.

Shadowlands can be found all along the west side of the Underground out-of-bounds area. The speciality about Shadowlands is, that you have to go in a certain way to "activate" them or you will not see them.

They have only been observed on PS3 (checked and not found on PS4 or PC versions).

Shadows in other OOB levels
A similar effect can also be observed in Pink Desert OOB (see video in the gallery below).

Guide Video
Unfortunately there are only a few videos about Shadowlands. You might find another way to get to Underground Shadowlands on Tara's Sky Journey channel on YT. Read the description of the video!

In Shadowlands at timestamp 12:10 minutes.

Images and Map
The image below shows how Shadowlands are structured (further explanations can be found in the image description if you click on it):

Shadows on ground in Pink Desert
At 5:16 mark, the stripes on the ground match the shadows found in the first carpet area in-bounds:

Trivia
Thus it's an empty "copy" of the actual level running in parallel to the real level along the west side of the map (and then wrapping again further north, this is why shadows of objects from the Friendly Tunnels can be found again in the golden-sand Tower area). Think of it as if the real level is one sheet of paper (north on top), to which another similar sheet is attached on the left side.
 * Based on the video, Shadowlands appear to be the result of terrain color/shadow texture tiling.
 * The nature of Shadowlands (texture tiling) suggests that there may be similar parallel "shadow land" further west, but this hasn't been tested.

Quotes
"A mysteriously beautiful place on the west side of UG oob. I go there from the end of the level."

- Stoicmom