Medellin for Christmas vacation? Si, si! The city once wracked by drug violence has undergone massive social and economic transformation, and it’s now known in tourist circles for spectacular Christmas light displays that veil churches, buildings, parks and even the Medellin River with glittering cascades of color. The spectacle can be seen in neighborhoods around the city every night through Jan. 12 from 6 p.m. to 1 a.m. It draws an estimated four million visitors, including thousands of tourists. The scene feels like a carnival, with crowds of families on foot gazing in awe, street vendors and long lines of cars and tour buses streaming slowly by.