In Spain and in many other parts of the world the cross is venerated. In May (officially on the 3rd) crosses are decorated. In UK and other parts of Europe (although not necessarily on 3rd May) a similar event occurs in the form of “well-dressing” which is believed to go back to pagan times and gives thanks for good sweet water.
For las Cruces de Mayo after they are decorated celebrations are held at them, often following a pilgrimage (una romería) bearing an image (often a statuette) of the Virgin of Sorrows (La Virgen de Dolores). A couple of years ago, we went on one that was held at Fuente Rueda up in the hills between Castillo and Valdepeñas de Jaén. Fuente is a spring or well, so this neatly combined the two cultures.
The photos were taken at that event.