Rise of the Tomb Raider

This is mostly self explanatory but I'll provide a couple of pointers for obtaining this.

This can be started through the Endurance Mode, selecting Co-op.

Any difficulty is allowed, I suggest Adventurer, the easiest.

Namely, one question I had was, you have to COMPLETE 10 days, ie reach the 11th day before extracting.

Helpful cards include Tomb Raider (for the codex skills which allow you to see traps in the tombs), either infinite fire or poison arrows (I had equal success with both).

Look for and pick up a lantern (usually near a settlement or basecamp) and keep this with you for guaranteed warmth at all times. Leave this at the entrance of a tomb or you will not be able to get it back up in most cases.

Pointer on finding Tombs/Crypts: always move AWAY from other landmarks you have found, we spread out from each other a bit and pretty much just ran in parallel in the same direction away from the bobcat until we found another Tomb.

In the Tombs, use Tomb Raider sense (or whatever it's called, press RS) frequently, this will help you avoid the traps (they show up red if you have the codex skills). All traps can be triggered ahead of time by arrows, this is recommended, especially the floor spike traps which seem to have a larger trigger stamp when not yet triggered.

This can be stacked with the other single player or co-op challenges such as Great Haul (10 days, 10 artifacts), the 7 day challenges (Bonding Time, etc.).