I can't confirm if these are all the locations, but I have found 53 locations in 24 different tiles
So far, I've done 24 consecutive missions without a new location

• Stribog, Void
  
• Marduk, Void

My cache guides:
Ceres, Corpus ship, Deimos, Earth, Grineer ship, Hive, Jupiter, Kuva Fortress, Lua, Uranus, Void

Tile 1
1
2

Tile 2


Tile 3
1
2


Tile 4


Tile 5


Tile 6
1
2

Tile 7
1
2


Tile 8
1
2


Tile 9
1
2

Tile 10


Tile 11
1
2
Inside the elevator


Tile 12


Tile 13
1
2


Tile 14
1
Under the stairs
2


Tile 15
1
2

Tile 16
1
2
3


Tile 17
1
2
3
4


Tile 18
1
2
3
4
5
6


Tile 19
1
2
3
4


Tile 20
1
2

Tile 21


Tile 22


Tile 23

Tile 24
1
2
3

I'll add a screenshot if I come across this in the future, or if someone can provide a screenshot


Some secretive places I've come across

1
Tile 11 - An open vent all the way at the top

2
Tile 15

https://youtu.be/j_Vx9gmeuYM

3 / 11 / 2022
Increased run count: now 24 runs without a new cache spawn

18 / 12 / 2022
Added location: Tile 9 2

12 / 12 / 2023
Added location: Tile 24 3 (currently recounting consecutive runs)