UCM (Universidad Complutense de Madrid) is the Complutense University of Madrid. With over 90,000 students, UCM is one of oldest universities in the world and is usually ranked amongst Spain's top universities. According to QS Top University Ranking, UCM is even ranked among the Top 50 most prestigious universities in the world for some of its subjects.
If you're interested in Politics, UCM is probably your best choice in the entire country. UCM alumni have been part of every Spanish government since the 18th century, so studying here is "getting your foot in the door" of Spanish politics. But there's more to UCM than Politics. Complutense is also a leading university for History and Languages, and prides itself on linking its research departments to its teaching.
It's really easy to get to Complutense, as it's in Madrid's main university campus: just take the metro's Line 6 to Ciudad Universitaria or hop on one of the many buses servicing the area (82, 83, 132, 133, 162).