The Soviets built a large underground bunker beneath the steel plant knowing the plant was a target for US missiles during the Cold War. The workers could escape to safety quickly.
There have been internet rumors that there was a biolab there and people who didn’t go along with the Azov battalion would be taken there for experimentation. This part isn’t confirmed.
But the underground bunker is. So it’s a siege situation sort of like Masada in Roman times, only not on a mountain but under the ground.
Thank you.