La Placita is the produce and meat market of Santurce by day and the most concentrated late-night drinking scene in San Juan by night. The market hall, built in 1910, anchors a small plaza ringed by bars — El Boricua, La Cubanita, Trastevere, and a dozen others — that spill onto the streets when the produce stalls close at sundown.
Thursday through Sunday is the time to go; by 10 PM the square is a wall-to-wall party of locals and visitors with live salsa and reggaeton coming from multiple directions. There is no cover, prices are reasonable, and the cabs back to your hotel are easy to find. Go in shoes you can salsa in.