How do Professional Game Companies Make Their Scenes/Worlds?

In “professional” 3D games such as Call of Duty, Assassins Creed, and so forth they have rather large worlds, especially AC. How do they make these worlds? I imagine it would take a nutso amount of time to make them in something like blender but what do I know. And if they do make it in blender or something else, how do they create things that you can interact with such as a moving elevator or a button that opens a door?
Thanks,
-cMp