The HYDRA Siberian Facility is a facility operated by the HYDRA branch inside the Russian Armed Forces, that contained the Winter Soldier and served as the main compound of the Winter Soldier Program.
Bucky Barnes, a former Howling Commando who was captured by HYDRA while trying to apprehend Arnim Zola, a HYDRA scientist, was kept their prisoner for many years until Zola, who was incarcerated by the SSR, was released from custody. Wishing to continue experimenting on him, Zola and other HYDRA scientists presumably took Barnes to the Siberian HYDRA facility where they replaced his missing limb with a prosthetic arm and turned him into a HYDRA assassin. For the next several decades, Barnes was activated to assassinate anyone who posed a threat to HYDRA. After successfully completing his missions, his mind was erased and he was put under deep sleep by HYDRA to ensure that he would feel remorseless towards those he killed, making him one of the most dangerous assassins in the world.
On December 16, 1991, Bucky was revived from a Cryostasis Chamber by HYDRA at the Siberian Facility and subsequently put under the Memory Suppressing Machine to wipe his memories and emotions. During his brainwashing session, Colonel Vasily Karpov recited his trigger words from the Winter Soldier Book to activate his brainwashing and training. After the Winter Soldier became obedient, Karpov ordered him to intercept a vehicle carrying a case of the Super Soldier Serum with no witnesses. On his mission in Long Island, New York, Barnes crashed the vehicle and ensured the Super Soldier Serum was safe before proceeding to kill its occupants, Howard and Maria Stark, and staging it to look like a car accident. Afterwards, Barnes returned to the Siberian Facility with the case in hand to deliver to Karpov.
At the Siberian Facility, HYDRA assembled five of the most elite assassins for the Winter Soldier Program with the new Super Soldier Serum. After being injected with the serum, the five assassins began transformation without the use of Vita-Rays at the expense of excruciating pain. Afterwards, Karpov put the Winter Soldiers through training with Barnes to test them. During a sparring session between Josef and Barnes, Josef managed to overpower Barnes despite his robotic arm, proving the Super Soldier Serum to be a success. Suddenly, the Winter Soldiers lost control and became aggressive and hostile to their HYDRA handlers. In response, HYDRA put all of them in Cryostasis Chambers. After the dissolution of USSR in 1991, the HYDRA Siberian Facility was abandoned with the Winter Soldiers still under suspended animation.
Almost 25 years later, Helmut Zemo swore revenge against the Avengers for the death of his family in the Battle of Sokovia, and sought to destroy them from the inside. After instigating the Bombing of the Vienna International Centre and the Clash of the Avengers, he led Captain America, Bucky Barnes, and Iron Man to the HYDRA Siberian Facility, under the threat of releasing the Winter Soldiers. However, when the trio arrived, they found that Zemo had shot all of the Winter Soldiers still under suspended animation. Zemo explained that the Winter Soldiers were merely to motivate them into coming to the Siberian Facility, and he explained his year-long hatred and obsession with the Avengers for their role in the death of his family in Sokovia. Zemo then revealed archive surveillance footage of the assassination of Howard and Maria Stark to Tony, revealing Bucky to have been his parents' killer. Outraged, Iron Man began to fight Captain America and Bucky, attempting to kill the latter. Captain America tried to explain that he was under mind control by HYDRA, but he ignored him and blamed him for killing his parents. During their brutal fight, Bucky tried to pull out Iron Man's arc reactor with his robotic arm, until Iron Man destroyed his arm with his unibeam and incapacitated him. Left alone, Captain America confronted Iron Man, deflecting his repulsor blasts with his shield.
Elsewhere at the Siberian Facility, Black Panther, who had followed Iron Man to the Facility, confronted Zemo, who remarked that he almost killed the wrong man due to Zemo's machinations. Zemo explained that his family was killed during the Battle of Sokovia, and to exact vengeance, he could not outright kill them, but he could manipulate them into killing each other. Then, he apologized for killing King T'Chaka, who seemed to be a good man who raised a dutiful son. T'Challa realized at how vengeance had consumed Zemo and was consuming Rogers and Stark, and swore off vengeance, deciding to spare Zemo. With his plan successful, Zemo attempted to commit suicide, but T'Challa stopped him and arrested him.
Meanwhile, Captain America continued to fight Iron Man, who had pinned him to the wall and furiously attacking him with his shield and fist. However, F.R.I.D.A.Y. had quickly analyzed his fight pattern and Iron Man gained the upper hand again, beating him bloody and throwing him across the room. Iron Man ordered Captain America to stand down, but he refused. As Iron Man prepared to fire his repulsor beam at him, Barnes distracted him and allowed Captain America to throw Iron Man to the ground. Captain America proceeded to beat him and smash his helmet off with his shield before destroying his arc reactor, disabling Stark's suit and winning the fight. Exhausted, Captain America picked up his shield and helped up a severely injured Barnes. Stark taunted Captain America that his father made his shield and he doesn't deserve it. Distraught, Captain America dropped his shield and left the Siberian Facility with Barnes.