Universal Studios is more about seeing than doing (as in riding a ride). There are many exhibits showcasing their productions (for example, the I Love Lucy store/exhibit). There is also a tram ride that provides a fun way to look at their movies that have been made there. This is a great picture place, providing lots of backdrops and nice scenery in the form of famous movies and shows. However, I don't think there's enough to do to last the whole day, unless the summer lines are really long.
As an added bonus, after you're done with the park, you can visit Universal Citywalk, located right outside the gates of the theme park. Another great tourist attraction, it provides street performers, some good eateries, and good people-watching. There are also several movie premieres held here.
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