In a tiny northern Chilean town in the driest desert in the world, 200,000 people are gathering this week for one of the most remarkable, vibrant, and little-known Catholic feasts in the world.

Every year, for 10 days surrounding the feast of the Virgin of Carmen, devotees, mostly young people, dance in brilliant costumes as a sign of their devotion to their Mother.

La Tirana, normally home to a thousand residents, is mostly comprised of confraternity dormitories built for the feast. Some are concrete and well-built, but many are cobbled from makeshift materials.

Empty most of the year, these buildings – indeed, the whole town – suddenly bulge far beyond their seams. Dormitories open and display each group’s image of the Virgin del Carmen at their entrance. Beyond the inhabited area of town, vast stretches of land are given over for tent encampments for the many dance groups that don’t own or rent dormitory space in town.

Members of the dance confraternities save, fundraise, practice their dances, attend retreats and plan for six months or more to get here.   The dancers and the many helpers and family who accompany them bring food and materials by bus and truck, and spend days opening up houses and setting up camps.

Dance confraternity members live in close quarters for 10 days, share meals in common, visit each other, and dance for the Virgin of Carmen in the church and its plaza in marvelous costumes.

Though July is winter in La Tirana – freezing in the unheated dormitories at night but temperate during the day – this is the time when confraternity members use up most of their annual vacation.  They travel from northern coastal cities such as Iquique, Antofagasta and Arica.

Almost all members, one leader explained, are “from the lower half” of society, and the cost of attending, hiring a band, making costumes, etc. constitutes a real financial sacrifice.

Whatever the cost, dancers say it is a great joy, and they vow to the Virgin to return and dance for a set number of years, as well as bringing their children back as they grow up.

Each dance confraternity gets several occasions to dance for the Virgin, beginning with a 20-minute “entry” when they dance before the image of the Virgen of Carmen inside the church. It takes four days, 24 hours a day, except during morning Masses, to accommodate all the groups.

After a group’s entry, they can dance with their own image of the Virgin in the church plaza or streets surrounding it, again according to schedule.

In a week full of “peak” events, the high point of the feast is probably the night before the official July 16 feast day. Only a small portion of the participants can fit in the plaza for the outdoor Mass and vespers, but the space is full.

Following vespers, the countdown to midnight grows raucous.  As temperatures drop near freezing, people are led in calls of “Viva la Virgen del Carmen,” wave balloons, and light flares and orange lanterns that float into the sky like tiny hot air balloons. The band near the outdoor altar plays music, and fireworks surround the city.

It’s much like New Year’s Eve in many cities, and participants sometimes described it that way, as the hinge point in their year.  From midnight until dawn, the confraternities in each association gather throughout the city to dance before the Virgin, to share food, and to celebrate. The town is alive all night.

The feast day is quieter. Its highlight is the lowering of the image from the façade of the church and a slow procession of the main image of the Virgin through the streets.

In the four days following the feast, dances continue in the plaza, and each group has a chance to dance a “goodbye” to the Virgin in the church. These are often especially emotional. On leaving the church, dancers always process out backward on their feet or knees, so as not to turn their backs on the Virgin.

Given the isolation of the spot and the lack of any real tourist infrastructure, few outsiders get to see the events, though many people from nearby cities do make day trips. For anyone from outside, however, the costumes of the dancers are almost incomprehensible: Gypsies, various Native (North) American tribes, devils, and polar bears among them.

How those came to be is a story in itself. To the dancers, though, the costumes are sacred, and cannot be danced in on any other occasion.  Neither can they eat, smoke, drink, use a cell phone, or take a selfie in them. Dancing devils may seem hardest to explain, but participants say they teach a lesson: They may trounce around in our lives, but even the devil always ends up having to bow down before the Virgin’s power, as they always do in the dances.

Dancers and association leaders alike insist that the costumes and dance, “secular” as they may seem, are not folklore. Lay heads of the dance associations draw careful boundaries between “carnival” and sacred dance, relying on behavior in costume, the cut of the dress, the attitude of the dancers, the presence of images of the Virgin, and more. Alcohol is not allowed in town during the feast.

Even the dances in the plaza and streets are taken as devotional events. For those dances, each group brings its own statue of the Virgin to a designated area at a designated time, and dances in a long line before her. Observers never clap for the dancers, and avoid walking between the image of the Virgin and the dancers honoring her.

Lay associations regulate most of the goings on, in cooperation with the clergy. Just organizing the times and locations of the dances is a big task, but volunteers from the dance groups insure water supply, sanitation, and almost every other civic need of the town during the feast.

Popular as the devotion is in the north of Chile, it is barely known in the distant central and southern parts of the country. A Santiago resident whom I traveled with said that she couldn’t fathom anything like it back in the city, but here it is central and taken for granted as part of Catholic life.

For the dancers, religious dances are regarded as a form of prayer, even an ideal form of prayer. As one dancer told me, “We are told that a person who sings prays twice. The one who dances prays three times.”

The people dancing for the Virgin are not removed from the scandals that plague the Church in Chile today. Indeed, several years ago, a bishop who had grown up in a family of religious dancers was removed because of an abuse allegation. But their sense is that this is their own feast, their way of honoring the Virgin and fulfilling a promise.

They struggled for years in the first half of the 20th century for full recognition from the Church, and were finally embraced, but the power of their devotion is enhanced by Church recognition, not simply dependent on it.

At the moment, participation in the feast continues to grow. Thirty groups are on a waiting list to participate, and have to settle for a separate dance in October. The presence of so many young people here makes it hard to see how this devotion does not have a strong future.

Thomas M. Landy is Director of the McFarland Center for Religion, Ethics and Culture at the College of the Holy Cross.  He leads the center’s Catholics & Cultures initiative, which explores the variety of Catholic practice around the globe.