Centro de Interpretación del Castillo de San Cristóbal

This free interpretation center sits right in the Plaza de España, built over the foundations of the 16th-century Castillo de San Cristóbal, once the main defensive fortress of Santa Cruz. You can walk among the actual ruins, check out a couple of original cannons, and get a solid sense of how dramatically the city has transformed over the centuries. It's a surprisingly gripping slice of history hiding beneath one of the busiest squares in town. Open Monday–Saturday 10am–6pm, with closures on major holidays and Carnival Tuesday.