"What are all those people doing?" This is probably the most common reaction upon stumbling onto the botellón. People of all ages (but tending towards under 40) gather in a public space, toting plastic bags bearing substantial weight. They contain bocadillos (sandwiches) wrapped in foil and litros (liter-sized plastic soft drink bottles) whose contents have been replaced at least in part by hard liquor. In San Sebastián, the seats lining the port are the most popular spot for the botellón.
In a botellón there are (almost) no rules...just have something to drink and a friend, or two, or ten. And let the night begin.