In addition, the city has about 160 museums—the world's greatest single metropolitan concentration —over 100 art galleries, and some 30 concert halls, all of which maintain a constant cultural activity during the whole year. It has either the third or fourth-highest number of theatres in the world after New York, London and perhaps Toronto. Many areas (e.g. Palacio Nacional and the National Institute of Cardiology) have murals painted by Diego Rivera. He and his wife Frida Kahlo lived in Coyoacán, where several of their homes, studios, and art collections are open to the public. The house where Leon Trotsky was initially granted asylum and finally murdered in 1940 is also in Coyoacán.