Schematic 4

Schematic 4 is an unique story item that allows the player to build the Coaster, it was added to The Forest in v1.10.

Gameplay
The schematic can be accessed in the back pages of the survival guide, where all the story items you find are located. It is implied by the sketch that the structure is useful for traveling via riding the turtle shell.

More info required

Location
The fourth schematic can be found in the cave to the southeast of the map, near the two small islands. Once unlocked the player gains the ability to create the Log Track. It also has images related to turtles, as well as a Cross embedded into a turtle's shell.