San Juan's night is split across three districts that are ten minutes apart by car — the cobbled bar street in the old city, the market square in Santurce, and the hotel-and-casino strip in Condado — and none of them get going before about ten.
Calle San Sebastián, Old San Juan
The bar street of the walled city, narrow and cobbled, running behind the Plaza San José. It is the default first stop for visitors and busiest Thursday to Saturday; it is also the focus of the San Sebastián street festival in January, when the quarter is impassable.
La Placita de Santurce
A working produce market square by day that turns into an open-air drinking district in the evening, with bars around the plaza and the crowd standing in the street. Salsa and reggaetón, a mostly local crowd, and cheaper than Old San Juan.
Condado — Ashford Avenue
The beachfront hotel strip east of the old city, where the night is hotel bars, rooftops and casino floors rather than street drinking. La Concha at 1077 Ashford Avenue is the anchor; expect resort prices and a dress code at some doors.
Isla Verde beach bars
Further east towards the airport, Isla Verde's hotel and beach bars run later and looser than Condado and suit an evening that starts on the sand. Practical if you are flying out early or staying near the airport.
Plan the hops, not the venues
Old San Juan, Santurce and Condado are separate districts with no useful late-night public transport between them, so budget for ride-hailing and pick one district per night rather than trying to cover all three. Bars fill from around 22:00 and La Placita peaks near midnight.