SAN JUAN, Puerto Rico’s nearly 500-year-old capital, is far less predictable than other Caribbean vacation spots. Restaurants with Michelin-starred chefs vie for your attention with hole-in-the-wall cafes, slick hotels with colonial fortresses, white-sand beaches with provocative street art. Dense rain forests and groomed coffee plantations lie a short drive away. Puerto Rico fell off many travelers’ radars after Hurricane Maria tortured the island in September 2017, wiping out thousands of lives and homes, denuding flora and laying waste to the power grid—and the recovery has been difficult. But today in San Juan,...