(National Theater Dona Maria II)
One of Lisbon's most popular hangouts is Dom Pedro IV Square -- more commonly called Rossio Square. It's been one of the city's main squares for centuries and remains a very busy place. It's a good spot to grab a seat and people watch.
The square is known for its wave-patterned tile pavement, originally created in 1848. I found the pattern to be eye-catching and photogenic.
Located across from the square is another popular landmark, the neoclassical National Theater Dona Maria II. It was built between 1842 and 1846 and hosts seasonal classical plays. Limited tours are given at the theater, so check the schedule if you are interested in seeing the interior. I think it would be very beautiful, but during this trip we didn't have a chance to.