Bolshoi Theater is one of the sites you must visit in your trip to Moscow. It's one of the most famous theaters in the world, not only for its architecture but for being the home of one of the most prestigious and oldest ballet companies in the world: The Russian National Ballet! It's also famous for including great operas in its program.
The best to experience the authentic atmosphere of the theater is to visit it for a ballet performance, an opera or a play. You can book tickets online but they're much cheaper at the box office!