Every other October, men and women climb on top of each other's shoulders as part of the Concurs de Castells in Tarragona, Spain. It's the ultimate exhibition of teamwork as large groups of everyday people from the ages of five to 95 work together to build a living human structure.

Dress is a vital element to the Concurs De Castells competition. Members of each team all wear the same bright color with a "faixa", or a black sash, that holds it all together. Despite just looking good, the faixa actually provides the crucial back support needed and the length is equal to one's position in the tower. A shorter faixa, which is 2 meters wide, is reserved for the light and nimble tower climbers, while faixa of up to 12 meters long provide the ground level team members with extra support. Wrapping the faixa is a pre-game ritual and a serious undertaking. Climbers go barefoot to help with agility and to go easy on the rungs of the human ladder.

Unlike the typical human pyramids, human tower building is a dance, based on order, method and ritual. It requires strength, balance, courage and common sense. The base, referred to as the "pinya" is usually made up of the strongest men, who also act as a safety net if the Castell collapses. Their arms are locked to create a strong foundation, and once it's been created, a signal strikes and a band plays the traditional song "Toc de Castells", to start the construction of the tower.

Concurs de Castells was recently recognized by UNESCO as one of the Masterpieces of the Oral and Intangible Heritage of Humanity, and is more popular than ever. Tickets must be purchased by travelers and spectators of the event. In addition to the pillars of people, the festival puts local cultural and entertainment on display with a parade of dance, music, concerts, fireworks and street performances.