While Madrid possesses modern infrastructure, it has preserved the look and feel of many of its historic neighbourhoods and streets. Its landmarks include the Plaza Mayor, the Royal Palace of Madrid; the Royal Theatre with its restored 1850 Opera House; the Buen Retiro Park, founded in 1631; the 19th-century National Library building (founded in 1712) containing some of Spain's historical archives; many national museums, and the Golden Triangle of Art, located along the Paseo del Prado and comprising three art museums: Prado Museum, the Reina Sofía Museum, a museum of modern art, and the Thyssen-Bornemisza Museum, which complements the holdings of the other two museums. Cibeles Palace and Fountain has become one of the monument symbols of the city.
Given this paragraph about the city of Madrid, what are the main landmarks of the city?
The main landmarks of Madrid include the Plaza Mayor, the Royal Palace, the Royal Theatre or the Retiro Park. Madrid also has many national museums, such as the Prado Museum, the Reina Sofia Museum or the Thyssen-Bornemisza Museum.