The Museum of the Rockies is a museum located in Bozeman, Montana and affiliated with Montana State University. As the name suggests, it is a museum dedicated to both the natural and cultural history of the nothern Rockies region.
There are many museums in Montana. Every small town seems to have one, and they mostly have local artifacts that are mostly of interest to other Montanans. Things like albino skunks and rusted tea kettles. Things that are more interesting to look at than snow, but might not be of interest to the wider world.
And as mentioned, The Museum of the Rockies does have exhibits of cultural artifacts. But what it is best known for is its natural history collection, where "natural history" means "Dinosaurs". Central and eastern Montana is one of the world's prime areas for dinosaur fossils, dating to the Jurassic and Cretaceous, when the area was the shoreline between the Rockies and the vast continental sea that covered what is now the great plains. And the dinosaurs there were not just some boring old hadrosaurs or chicken-type things: they were the grand, charismatic dinosaurs that graced our young minds, Tyrannosaurus rex and Triceratops. Which means that the Museum of the Rockies, situated in the small college town of Bozeman, ended up having the world's largest collection of Tyrannosaurus rex fossils in the world. As well, as of course, various other specimens. It is also the institution where Jack Horner, one of the world's leading paleontologists, does his work.
In other words, if you are interested in dinosaurs, even a small amount, and happen to find yourself passing through Montana, you should definitely make a stop at the Museum of the Rockies.