The Endurance Mode is one of the DLC Expeditions in Rise of the Tomb Raider, that can be selected from the main menu. It is part of the Season Pass, the 20 Year Celebration and can also be purchased individually.
Lara is searching for Artefacts in Siberia when her Snowcat breaks down. She is forced to survive under harsh conditions by Hunting game and staying warm at Base Camps or other fire. She can be extracted from the wilderness at any time by lighting one of the Signal Fires, which will alert a helicopter to her position.
While in the wilderness she repeatedly encounters Deathless and Trinity soldiers, but wild animals like Bears and Wolves also make her survival more complicated. When night falls or a storm hits, temperatures drop significantly and it is best to head for shelter. All the while she has to look out for Ruins and Crypts where artefacts might be hidden.
During Lara's expedition in the Siberian outback there are two gauges displayed on the screen, one for food and one for warmth. If either of these drop to zero Lara will die, either by starvation or by freezing to death. The only way to keep these meters up in the green is by hunting animals or gathering other edibles like berries or cans of food left behind by other expeditions; and by keeping warm at a fire or by carrying an Oil Lamp around respectively.
To light a fire at a base camp Lara needs Hardwood and Cloth, so gathering Resources is another part of this expedition mode. Wood and cloth is also needed to light the signal fires. These do not only call the extraction helicopter but also attract all kinds of Enemies.
As with all Expeditions the player can choose from a wide variety of