The great forts — San Juan's defining sights are its two vast Spanish forts. El Morro (Castillo San Felipe del Morro) juts out on the headland at the tip of the old town, a six-level fortress of ramparts, ramps and lighthouses rising from the sea cliffs, with a huge green esplanade in front where kites fly — a stunning place, especially at sunset. Across the old town, Castillo San Cristóbal is even larger, guarding the landward side with tunnels and bastions. Touring the forts, walking the ramparts and grasping how they held the Caribbean's gateway is the essential San Juan experience.
The blue-cobbled old town — Between the forts, Old San Juan is a joy to wander — narrow streets paved in the distinctive blue-grey adoquín cobblestones, lined with colourful colonial houses in pink, blue, yellow and green, opening onto shaded plazas, churches and the city walls. Walk the walls and the Paseo de la Princesa along the water, see the cathedral and La Fortaleza (the governor's mansion), and soak up the colour and life. It's compact, beautiful and lively, and full of cafés, shops and — come night — bars and music.
Beaches and the Caribbean — San Juan is a beach city too — just east of the old town, the districts of Condado and Isla Verde have golden Atlantic beaches, resort hotels and a seafront scene, with the calmer Ocean Park in between for a swim and sun. Beyond, the island's beaches, rainforest (El Yunque) and offshore cays are within reach. Between the history of the old town and the sand of the beach strips, San Juan lets you mix culture and coast easily in a day.
Food, rum and music — Puerto Rican food and music are a highlight. Eat mofongo (mashed fried plantain with garlic and pork), lechón (spit-roast pork), arroz con gandules (rice with pigeon peas), alcapurrias and tostones, at the lechoneras, the Santurce market and the old-town restaurants. Drink the piña colada (invented in San Juan) and Puerto Rican rum, and let the salsa, bomba, plena and reggaeton carry the warm nights — Calle San Sebastián in the old town and La Placita in Santurce are the party hearts. The food, rum and rhythm are the island's soul.