Spain is one of four countries, along with Bosnia and Herzegovina, San Marino and Kosovo, whose national anthem is wordless, Giles Tremlett points out in the introduction to his beautifully illustrated Brief History of Spain (Head of Zeus) published recently.
This anomaly came to international attention at the opening of the 2010 World Cup final in South Africa between Spain and the Netherlands when the Spanish squad, to the bemusement of spectators and the Dutch team, merely hummed along to the music.