Opening its first line in 1935, the Moscow Metro was a big deal from the start, representing not only a feat of engineering, architecture and construction, but also a PR tool for communism at a time when capitalism seemed mortally wounded by the Great Depression. Featuring elegantly designed stations with marble columns and exquisitely detailed ceilings and light fixtures, Moscow's magnificent new metro (so the story went) was but a taste of the glorious future the Soviet system would deliver.
That didn't end up working out too well. But the progressive crumbling and ultimate collapse of the USSR didn't take any of the shine off of the capital's underground transit system. Expanded in multiple stages after its inauguration, today the Moscow Metro is the fifth-longest metro system in the world and carries more passengers than any other system outside of Asia. Moreover, the opulent design of the stations–which grew in subsequent stages to include chandeliers, painted rotundas, and fine works of art–makes the system an attraction independent of its role as a means of transportation. You can even visit a museum covering the history of this remarkable specimen of urban planning and socialist realist aesthetic–if you know where to look.
From southern end of the lobby of the Sportivnaya Metro station, there is a stairway to the third floor ("through a room where police are checking documents, past those that are detained") which houses a free museum dedicated to the history of the Moscow Metro. Inside are photographic exhibits showing the construction of various stations and railways; celebrations from the opening of the system; uses of the stations during wartime for sleeping, meeting, and taking shelter; and other aspects of the system's history.
Beyond the photographs, the museum exhibits actual equipment from the Metro system, including different kinds of tracks and cabling, turnstiles, tokens, uniforms, a miniature model escalator, and even a section of a train car. You can push the buttons and flip the levers in a real driver's cabin, or try your hand at directing trains on several different generations of metro traffic control machinery. There is an exhibit with details on each particular type of train that has been used in the system, as well as exhibits on other metro systems across Europe. The museum is free.