Salón Tenampa has stood on the north side of Plaza Garibaldi since 1925. It is the cantina the mariachis built their reputation around - the singers and their bands have been making the plaza their open-air auditorium since the 1920s, and Tenampa is the room they walk into between sets. The right way to understand the bar is to spend a single night moving through its different hours.
Tenampa is not a hidden bar in any literal sense - it is one of the most visited rooms in the city and has been for decades - but the experience of an unhurried mariachi night here is one most visitors miss because they are intimidated by Plaza Garibaldi's reputation. The plaza is fine. Take a taxi door-to-door. Stay until 11pm.