Walking across the Plaça d'Espanya, it is hard to imagine that there is a vast space below ground. The work of architect and engineer Santiago Calatrava, from 1992 to 1995, this immaculately white underground cavern with parabolic arched ceiling (a favourite technique of Calatrava's) hosts temporary exhibitions. Access from the Plaça de España is via the lift beneath the Casa Consistorial, on the left of the passage leading to the Plaça de Dins.