There used to be a marble quarry near that area which is where "Carthage Marble" came from... many historic buildings in the Ozarks, and other parts of the world, are supposedly built with Carthage Marble. The Courthouse in Carthage is, as well as several historic houses in the city.
Americold Logistics (as someone stated) has storage there, Leggett & Platt did (not sure now), as did Schriebers (cheese, condiments, etc). Supposedly the government stores documents or some such there (they supposedly do that in most of the "underground" locations in the US. Springfield and KC for instance).
What would be more interesting to look into is a legend that I researched when I was young. Supposedly, there is a giant, natural cave ,lake, and river system under the city... probably just south of where the carthage undergound is. A Jr. High teacher in Carthage was doing research on it at some point, and had a run in with some individuals who didn't want the area to be found... entrances were found and sealed... etc. My hunch (speculation... completely) is that some entrances were found in the basements of one or more historic homes in the city which belonged to prominant families at some point and there was probably evidence that tied them to slavery or the klan.
Whether or not any of that is true, I am not sure. I heard and read things on more than one occasion that would lead someone to believe it, but you know how small town rumors are. Carthage really is a very interesting city. The downtown area is small, but it has always been a great place to read about and explore. There are small caves all around the outskirts of town, some where civil war battles supposedly took place. There are supposedly tunnels connecting many of the more prominent houses in town. Carthage was where the rich families lived that owned many of the mines in that part of Missouri.
Just thought I would share the bits of info/gossip/non-sense that I picked up when I lived there to help fuel the curiosity
Sorry for spelling errors 
