These days, Pripyat, Ukraine—the city rendered a ghost town by the Chernobyl disaster—is more or less safe. Still, there are a few places that are not recommended venture into. One of these places is the basement of Hospital 126. This is where citizens gathered to strip their clothes after the meltdown; these clothes are still there, and still highly radioactive. Some videos on Youtube document readings of over 600 millisieverts on these clothes; this is well within “get the hell out of here” levels.

But that’s still not an immediately dangerous amount of radiation; you can receive about the same amount every year, just from the sun. It’s now safe to walk through Pripyat and even most of the Chernobyl facility without any protection. But if it had not been for three volunteers, Chernobyl, Pripyat, and a huge part of Europe would be a radioactive wasteland today.

Beneath the critical reactor was a pool of water. This water was used as coolant for the plant—a pretty standard feature. But after the the explosion, all that incredibly radioactive nuclear fuel was chilling in the reactor. The gunky mixture of the sand and clay used to extinguish the fire and the still active radioactive fuel turned into a lava-like substance that began eating away at the floor. If the lava burned through the floor and fell on the metal, a massive explosion would occur—far larger than the original—that would make half of Europe uninhabitable for 500,000 years.

It goes without saying that preventing this explosion was imperative. Luckily, the pool could be drained, but only through releasing the valves in the basement, which was now flooded with extremely radioactive water. Narratives of the story differ after this, but the traditional tale is that three men—Valeri Bezpalov, Alexie Ananenko and Boris Baranov—volunteered to go into the basement and release the valves, knowing that it was a suicide mission from the start. They all died of ARS (Acute Radiation Syndrome) within weeks.

New information unearthed by author Andrew Leatherbarrow, however, tells a different, less epic, but still quite epic story. The basement, it turns out, was partially drained by firefighters. Surrounded the pitch black of the basement, they trudged through knee-deep radioactive water until they found the valves, knowing that every moment they spent in that water was more of their own DNA being destroyed. They ended up finding the valves and releasing the water, saving millions of lives. They returned to the surface. In 2016, one diver was found alive. Baranov died in 2005. No word on the third.

I like that version more. But either way, you’d be hard pressed to find a more heroic moment in human history. I mean, this is a pretty messed up world as it is, but can you imagine how much worse things could be if all of eastern Europe was uninhabitable? That’s a terrifying prospect, and one that would could be real without the bravery of these men. Thank y’all; we all owe you. And a happy holidays to everyone, because apparently nothing says holiday spirit like a devastating nuclear event. So be thankful this weekend; it could always be worse.