If you are interested in modern art, you will find it in the somewhat unlikely setting of the 18th-century Zamek Ujazdowski, reconstructed in the 1980s. The castle hosts a variety of temporary exhibitions by artists from Poland and all over the world. It is home to the most comprehensive permanent collection of Polish contemporary art found anywhere in the country (still growing, by its very nature). You can easily spend a day there, catching a leture, a movie (in the summer outdoor cinema), or lunch (at a cafeteria or a more fancy restaurant within the castle gates). The bookshop is well stocked with art publications and souvenirs.
ul. Jazdów 2, Warsaw, 00-467, Poland