Level Keys
"You open a drawer in Level 1's depths. An old key. You haven't seen this before. Picking it up, you feel strange vibrations coming from the object. It makes you dream of another land…"
Description

Level keys.
Level keys are objects exclusively found in Level 1, albeit this is incredibly rare as you could open thousands of drawers in the level and not even find one. Each key links to its own level and will vibrate softly in the closest direction to its level, if the level is not accessible (or the closest entrance to the level is The Hub), it will vibrate towards the closest path back to Level 1, and then The Hub. Some levels do not have a key, these being Kitty's House (A2), The Hub (A3), and The Shady Gray (A4). Level A1 does have a key however, but this is likely due to how it is intertwined with most levels. Sublevels and negative levels are missing keys too.
Each level key has a different appearance and does not tell you which level they lead to directly. The keys however, do represent what kind of key you'd expect to find within the level in which it belongs to, so it's not incredibly hard to figure out who it belongs to if you have knowledge of all the levels.
Sleeping next to a level key will cause you to dream about the level it belongs to, so that's another way to find out if you are really stumped.