There is no sign. You look for the worn corner building on Calle San Sebastián, push the door, and find a dim room with a chalkboard menu and a bartender who knows what they are doing. That is the first bar. Behind it, through an unmarked doorway, is a second, and beyond that a wine bar, a dance floor and a couple of rooms most visitors never reach. La Factoría has been on the world’s best bars lists for years and has stayed refreshingly unfussy about it. Order the Lavender Mule, the house drink and the one everyone remembers, or let them read you and build something. Drinks are properly made and the room fills with locals as much as travelers. Arrive before nine if you want a seat and conversation. After eleven the back rooms open up, the salsa starts, and it becomes a different night entirely. Calle San Sebastián is the spine of Old San Juan’s nightlife, so if it is full there are ten more doors within a hundred meters. Cash and card both work. Take a taxi both ways from Condado, about fifteen minutes, and do not plan an early start the next day.