Parque Calderón is the city's main plaza, dominated by the Catedral de la Inmaculada Concepción, the 'new cathedral,' whose giant sky-blue domes are visible mainly from the rear of the church. Inside, the marbled interior is rather stark. Construction began in 1885, and the cathedral was supposed to be much taller than it is - an error in design meant that the intended bell towers could not be supported by the building.