Palacio de Cristal/Retiro Park
Retiro Park, often referred to as the city's "green lung," is certainly a vital organ for Madrid. Thousands of locals jog its perimeter every day, while others can be found strolling its leafy paths. There is a lake for rowing, restaurants and outdoor cafés, children’s playgrounds, and the picturesque iron-and-glass Palacio de Cristal. Built in 1887 to house exotic plants, it's now the site of cutting-edge contemporary art installations organized by the Reina Sofía Museum.