Cobbled Calle Mercaderes between Obispo and Plaza Vieja [1], four blocks south, is full of attractions. Not least is the Maqueta de la Habana Vieja (Model of Old Havana, Mercaderes #114, tel. 07/866-4425, daily 9:30 a.m.–6:30 p.m., entrance CUC1, guide CUC1, cameras CUC2, videos CUC5). This 1:500 scale model of Habana Vieja [2] measures eight by four meters, with every building delineated and color coded by use. Guides give a spiel.
Links:
[1] http://www.moon.com/destinations/cuba/havana/sights-habana-vieja/plaza-vieja
[2] http://www.moon.com/destinations/cuba/havana/sights-habana-vieja