The ancient chest has appeared next to the Ancient Pseudoscience Station, it accepts 6 items (similar to how our part two puzzle was 6 slots), and requires the right combination of items. YOU AND YOUR PARTNER BOTH NEED TO BE NEAR THE CHEST.

If you want to teleport there, go inside the caves with your partner:
c_gonext("sacred_chest")
c_gatherplayers()

The following are confirmed:
Quantity of items
= 1 = 2 = 3 = 4 = 5 = 6 = 7 = 8 = 9

The item
= Walking Cane (This is present in every single solution code).
= Thulecite (This is present in every single solution code).

= Purple Gem = Crow = Nightmare Fuel = Petals = Berries
= Yellow Gem  = Bee   = Carrot = Orange Gem = Rabbit = Butterfly

Item Prefab Listing

Here is an example puzzle and how to solve it!

The image shows us the position in the chest, Metheus Runes show us the item (left picture) the square-nooks give us our quantity (right picture). Our solution would be:
Walking Cane (1), Crow (1), Petals (8), Nightmare Fuel (4), Purple Gem (2), Thulecite (5).

Huge shout-outs to all the contributions from the community! WE DID IT TEAM!