San Juan gives you a walled Spanish colonial city with two working forts at one end, a serious art museum and a rainforest within an hour, and beaches you can reach on a city bus.
Castillo San Felipe del Morro and Castillo San Cristóbal
The two forts of San Juan National Historic Site, run by the National Park Service. One $10 ticket covers both and is valid 24 hours; under-16s are free and the park takes cards and contactless only, no cash. The lawn in front of El Morro is where the city flies kites.
Old San Juan on foot
The walled quarter is small enough to cross in twenty minutes: blue cobbles, the Paseo de la Princesa along the outside of the walls, and the Paseo del Morro path beneath them. Go early — it is hot by eleven and full of cruise passengers by noon.
Museo de Arte de Puerto Rico
At 299 Avenida de Diego in Santurce, open Wednesday, Friday and Saturday 10:00–17:00, Thursday 10:00–20:00 with free entry from 17:00, Sunday 11:00–17:00, closed Monday and Tuesday. General admission is $17, with resident, student, senior and military discounts.
Casa BACARDÍ, Cataño
The visitor centre at Carretera 165 km 6.2 in Cataño, open daily 10:30–19:00. The 50-minute Legacy Tour with tasting is $40 plus tax, with longer mixology and warehouse options up to $125. Easiest arrival is the ferry from Pier 2 in Old San Juan plus the shuttle, about 20 minutes door to door.
El Yunque National Forest
The only tropical rainforest in the US national forest system, roughly an hour east of the city by car. Access rules and recreation fees for El Portal and the La Mina area have been changing, so check the forest's own page for current requirements before you drive out.