Each December, Colombia’s second-largest city heralds the holidays with a month-long festival of Christmas lights, Los Alumbrados. It’s as though this once-violent city emerged from the dark cloud of drug violence that held it captive until three decades ago and celebrates its freedom anew each year with a great burst of light.

More than 30 million LED bulbs turn parks, gardens, streets, plazas and the Medellín River into a holiday fairyland that springs to life as darkness falls each evening. Christmas ornaments shaped from tiny lights hang from trees arching above streets, twinkling angels fly overhead, and scattered stars dangle in the air.

Parks become magic forests of sparkling trees, clouds of light float overhead, colored beams play across the hillsides surrounding the city, and arches of lights crown promenades and streets. In the Botanical Garden, walkways are lined with borders of fanciful electric flowers blooming in rainbow colors, their glow illuminating the tropical foliage overhead.

The mile-long stretch of the Medellín River between the Guayaquil and San Juan bridges gushes with illuminated water spouts, fountains bathed in lights that change color in time with music. Lights seem to float and spring to life as projections dance in the plumes of water. The reaction of wide-eyed children to this magical scene provides half the fun.

After wandering through the park alongside the river to see the dozens of giant illuminated Christmas scenes — some as tall as 75 feet — and other holiday-themed displays, board a chiva with fellow revelers to tour the city’s other lighted venues. These open-air buses are moving parties filled with strangers singing together and vendors clinging precariously to the outside as they sell cold drinks through the open windows.

Each park and square where the chiva stops hosts more vendors grilling savory sausages and selling fresh-cooked buñuelos (fried dough), roasted ears of corn and skewers of chicken or beef. All of Medellín becomes a citywide block party.

Everyone seems to get into the act. Lights decorate homes in residential neighborhoods while department stores and shopping centers throughout Medellín add their own elaborate indoor and outdoor displays. Office buildings in the city center and on the mountainsides above are bathed throughout the night in moving patterns of colored light.

Throughout the festival, which begins Dec. 1 and continues into mid-January, there are more than 500 different activities in various parts of the city and 80 special events that include concerts by the Medellín Philharmonic Orchestra, the Youth Orchestra of Medellín, choruses and other musical groups. These often take place in open-air venues, with both ticketed seating and free public areas. Lavish fireworks displays kick off the lighting and continue throughout December.