Like most of the best experiences we’ve had in the islands, finding the Hotel El Convento in San Juan, Puerto Rico, was nothing short of pure serendipity.

It happened to us just like it eventually happens to all Caribbean travelers. A squall delayed our flight from Anguilla and we missed the state-bound American Airlines connection in San Juan.

Puerto Rico, a U.S.-administered territory about half the size of New Jersey, sits east of the Dominican Republic just above the great arc of the Lesser Antilles. It was always one of those places we had meant to explore somewhere down the road, but had never quite gotten around to it. We knew from glimpses out airplane windows that it was a beautiful island with long white beaches and verdant rainforests rising to shark-toothed highlands. But we had always pictured the island as sort of an overlooked Caribbean stepchild, a fading Castilian past of cobbled plazas and seaside fortresses overshadowed by a U.S.-influenced present full of high-rise condos and American shopping malls.

Sometimes it’s great to be wrong. As we soon discovered in the second oldest city in the Americas (and a United Nations’ designated World Heritage Site), the past is alive and well and waiting to be discovered in Old San Juan.

Arriving at the Hotel El Convento was like stepping back in time—three centuries to be exact. That was when the building, originally a Carmelite convent, was constructed. The 58-room boutique hotel, a masterpiece of Old-world architecture and modern luxury, retains the atmosphere of the original fortress-like structure, complete with thick walls and a shaded courtyard greened with garden plants.

The classic and unpretentious ambience extended to our room where mahogany ceiling beams nicely accented the canopied bed, antique hand-crafted furniture and an elegantly marbled bathroom. Modern accessories were understated but handy—a full stereo entertainment system, TV and VCR, and dual-line phone with data ports.

Beyond the rooms, the hotel was a delight to explore. Fitness enthusiasts will enjoy the gym, complete with a treadmill, stair climber and free weights. And to combat post-workout soreness, you can indulge in a massage or relax in the rooftop pool and Jacuzzi with sweeping views of San Juan Bay.

Even with just a stopover in San Juan, it is possible to explore the colonial capital and immerse yourself in the city. After an hour-long guided walking tour that highlighted the centuries-old churches, fortresses and historic homes of the city, we wound up back on Cristo Street outside the hotel for some last-minute shopping. Antique shops huddle shoulder-to-shoulder with big-name outlet shops like Ralph Lauren, Coach Leather and Dooney & Bourke. Nearby El Galpon boasts an impressive collection of cigars, while GOA has a nice selection of Spanish ceramics and carved Santos.

Back at the hotel, we enjoyed cool mojitos at El Picote, a top-rated restaurant with a truly authentic setting overlooking the hotel’s open-air courtyard. We were delighted to see that the owners made an effort to preserve the hand of Father Time in the restaurant’s details—exposed brick patches in the peeling plaster walls had not been covered over, and modern light fixtures hadn’t replaced hand-blown lamps fitted with dripping candles. El Picote is open Tuesdays through Sundays for lunch and dinner. Another option for lunch is the Patio del Nispero in the courtyard below. Open daily for lunch, it is the perfect place for an alfresco meal.

The morning after our missed flight, we shared a gourmet breakfast in the Garden Terrace, overlooking the Plaza de las Monjas and the historic San Juan Cathedral. We sipped strong coffee and caught up on e-mails next door at the library. The front desk informed us that American Airlines had rebooked us on an early flight.

It was then we realized that instead of forced layover, our brief time at the Hotel El Convento and historic San Juan was a wonderful, unplanned adventure on an island full of ambience, history and culture. We’re already planning our next missed connection.