The Museo Nacional Centro de Arte Reina Sofía is Madrid's 20th-century art gallery and along with the Prado and the Thyssen-Bornemisza, makes up the city's trio of great museums. The museum contains more than 21,000 works of art, including pieces from Salvador Dalí and Joan Miró but probably the most famous work is found on the second floor. Picasso's "Guernica" is the museum's crowning jewel. 

As is the case with other modern or contemporary art museums, travelers say you'll especially enjoy Queen Sofia if you appreciate modern art. If you're not a huge fan, you might want to spend your time at the Prado or Thyssen-Bornemisza. 

The Queen Sofia Arts Center also has two exhibition spaces at Retiro Park. Tickets cost 8 euros ($9.30) if purchased in advance online and 10 euros ($11.60) at the box office. Note that you can skip out on the online admission price by visiting the museum during its free hours, which are Sundays from 1:30 to 7 p.m. (Only select spaces are open at that time.) Hours vary, so check the museum's website for details. On-site facilities include a cafe and museum store. You can reach the museum from the Atocha metro stop.