The 17th century Royal Ujazdów Castle houses the Centre for Contemporary Art, with some permanent and temporary exhibitions, concerts, shows and creative workshops. The Centre  realizes about 500 projects a year. The Zachęta National Gallery of Art, the oldest exhibition site in Warsaw, with a tradition stretching back to the mid-19th century organises exhibitions of modern art by Polish and International Artists and promotes art in many other ways. Since 2011, Warsaw Gallery Weekend is held on the last weekend of September.