I don't remember exactly when I read this, I think at least ten years ago, almost certainly more than five years ago. I don't remember what was being investigated in the story, but the protagonist is in a town that has a deserted military complex dating back to the Cold War just outside of town which I remember as just being sort of an airfield with buildings, but it's revealed that there's a massive underground complex underneath it. Everyone knows about the facility in town, but speculation is rampant about what the purpose is, with the military providing no answers. The climax of the book has the protagonist driving to the base during a winter storm with someone he believes to be his ally (law enforcement?) only to realize (or maybe have exposited to him) that this guy is actually part of the conspiracy. Noting that the other guy (who may have already pulled a gun) is not wearing a seatbelt, he chooses to crash the car. I think the other guy is killed, or at least knocked unconscious, but the next problem is that the car is no longer functional, and the temperature is dropping, so he breaks into one of the facility buildings. Something happens which results in a fire, or explosion, and the protagonist quickly realizes that the lack of ventilation meant that the oxygen in the facility would be deadly very fast, and so he proceeds to run up the stairs at high speed, with the text pointing out how impossible this should be with the wind opposing him (air being sucked in from above through the stairwell due to the fire pulling in oxygen), he just kind of escapes by Running Real Hard, which just felt very silly to me in a book which otherwise seemed reasonably realistic. Of course, the massive fire also keeps him warm long enough to survive for the arriving emergency response to pick him up.
I remember that one of the speculations on the purpose of the facility was that, due to the lack of apparent lighting, it was meant to provide care, or at least lodging, for people who lost their faces during the then-imminent World War III with its nuclear blasts, but I think the protagonist eventually learns that the intended usage was actually to shelter children in it so that the next generation would survive to rebuild, and the protagonist thinking back on his own misspent childhood, and musing on how the outcome was likely to be more Lord of the Flies than anything positive.
I am almost entirely certain this was a book in the middle of a longer series, but I've read so much pulp fiction over the years that it all sort of blends together. The book was in English, and I think was of a decent length (at least 200+ pages). I'm pretty sure I read it as a physical book rather than listening to an audiobook or reading an electronic copy, and that I probably checked it out of the library.