The Gulag is a part of the Soviet Installation Location in Rise of the Tomb Raider and one of two huge hub levels. The Name the Soviets gave the Gulag is Freedom Station. In the Baba Yaga: The Temple of the Witch DLC the Gulag is often only called by that name; in fact Serafima is very unhappy with this name.
Lara, on her mission to rescue Jacob, gets imprisoned in the old Gulag when she is spotted by Trinity soldiers. It is here that she finds out that her stepmother Ana is actually a Trinity operative that was planted in her father's household to spy on his research and manipulate him.
The Mission Gulag Recon leads Lara back to Freedom Station. She has to discover enemy troop movement plans, find the guard schedule for the Gulag, and finally reclaim the archaeological discovery evidence.
Baba Yaga DLC
In the Baba Yaga DLC we find out that Ivan was a guard in the Gulag and that his lover Serafima was a prisoner send here for throwing a drink in the face of a Soviet minister. Nadia, their granddaughter, heads here to find the old manifests which record the location of one of the ingredients to the Antidote for the pollen of the Dreaming Blossoms flower that grows in the Wicked Vale is located.