Travelers who visit the island of Samui, Thailand, may feel like they have stepped into a tropical postcard. The powdery white beaches, emerald forests, and secluded vistas present a picture-perfect paradise for romantic excursions, family vacations, or laid-back getaways.

Six Senses Samui, a 66-villa resort located on the northern tip of the island, reopened last week after an extensive renovation. The suites feature updated furnishings, and the bathrooms—which are air-conditioned and fully enclosed—have b…