Tribal Pass

This is unlocked by completing a run under "Start single run" option on the map. You have to make it through 5 levels in total to reach the end. Doing so unlocks the "Big Pass" mode, where the real ending takes place.

There are no special tricks to this, trial and error will help you know when and how to avoid dangers, keeping food stocks high, balancing how many tribesman you keep with said food stores, and picking and choosing what achievements to go for (cannibalizing or not, making it past a desert without starvation ect) are important for making it through a run.

You always have the option to quit to the main menu, which lets you retry the level you are on, and in many cases reseeds the map, giving you a new mix of challenges and food/firetender locations.

It will potentially take a few runs to get a feel for the game, but once you do, this isn't as hard as it first seems.
Due to the RNG nature of this game however, its difficult to write a step by step guide. The run I won didn't have any deserts or cold lands in my path, making it a breeze to keep food up. Just keep trying and you will net yourself this cheevo.
I will gladly answer any and all questions to help make this easier on you, however.

Happy hunting (>*_*)>