Concierge.com's insider take:
The limestone pillars of Thailand's Phang Nga Bay may have gotten the screen time in The Man With the Golden Gun, but for sheer spectacle, nothing compares to the sublime pinnacles of Halong Bay, 100 miles east of Hanoi. Many of the bay's 1,600 limestone islands and isletsthe world's most extensive karst seascapeare part of a protected 580-square-mile UNESCO World Heritage Site. Cruises are the best way to appreciate the bay and the fantastically shaped formations that erupt from the South China Sea. Dozens of companies offer daylong tours from Halong City; splurge for a longer trip and spend two or three days exploring. There are numerous sea caves and grottoes as well as the primeval Cat Ba Island, where a national park protects habitat for one of the world's rarest primates, the golden-headed langur. The most comfortable way to cruise the seas is on the 38-cabin floating palace operated by Emeraude Classic Cruises (59A Ly Thai To St., Hanoi; 84-4-934-0888; www.emeraude-cruises.com). Although the design replicates that of a French paddle steamer that sailed these very waters a century earlier, you'll get the full round of modern conveniences, from sunrise tai chi classes to sea kayaks to evening movie screenings on the open-air "star deck.'' With working sails to augment its engines, the junk-style Halong Ginger offers more rustic luxury (84-4-984-2807; www.cruisehalong.com).
Cool, misty weather swathes Halong from February to April; depending on your taste, this can make the bay a bust, or even more magical. Check your boat company's cancellation policy; in the summer and fall, storms and typhoons can prompt authorities to temporarily close the bay.