While we were driving home from DF there were lots of people bicycling on the road. At first we thought it was some kind of race, but that didn't make sense since the bikers didn't really look like racers, and there were a lot of people totally flopped on the ground at the end of the group who didn't look like they'd make it much further. As we went along, we passed several portable shrines that the bicyclers were following and we remembered we were going toward a pilgrimage site that we'd passed on the way there. We guessed that instead of a race, we were seeing a bicycle pilgrimage, which we'd never heard of, but it made sense, especially since it was a few days before Lent.
So, as usual, the internet took all those clues and gave us San Juan de los Lagos. Its church with its image of the Virgin is the second-largest pilgrimage site in Mexico and some of those pilgrims do arrive on bicycles. I couldn't find the camera in the car while we were driving by, unfortunately, but maybe we'll see them again sometime. Major pilgrimage days/months are Candlemas, May (Mary's month), August 15 (Mary's Assumption), and December 8 (the Immaculate Conception).