At the 24th annual Tarragona Castells Competition in the small town of Tarragona southwest of Barcelona, members of Caprogossos de Mataro, a team of "Castellers" as they're called in Catalan, build a human tower. Teams like this travel to festivals in the region and compete to build -- and, when possible, dismantle without collapsing -- the highest and most complex tower. This year, more than 30 groups built towers, some involving more than 400 people, with many of them standing at the bottom to add support to the foundation. More than 7,000 people came to watch the festival this year.