The 300 block includes the oldest existing bookstore of El Ateneo chain (one of two on Florida Street); founded in 1912, the booksellers opened their first Florida Street store in 1936. Facing El Ateneo is the former headquarters of "La Nación" newspaper. One of numerous Plateresque office buildings completed in the area during the 1920s, the building, known today as the Mitre Gallery, is the second store opened on Florida Street by Falabella. The corner of the intersection with Avenida Corrientes is overlooked by office high-rises, a Stock Center sporting goods megastore, and, for contrast, the former Elortondo Alvear residence (1880); the neo-Gothic mansion was converted into a Burger King in the 1990s.