Low clouds scudded across the sky as our little boat glided over the emerald water. From time to time fisherfolk waved at us from passing sampans, and occasionally we spotted a stately junk, its sails silhouetted against the horizon like the wings of a giant butterfly. A few birds, unable to restrain their curiosity, brazenly darted down to inspect us. Except for the sputter of our primitive engine, the scene was strangely silent. A faint, late afternoon breeze stirred, portending the end of the day. Then, as it does in the tropics, the sun suddenly set in a riot of red, and we returned in the reflection of its fiery glow.¿I have been zigzagging around Ha Long Bay, a panorama of 1,600 islands mysteriously sculpted by nature, resembling pyramids, pillars, cones, humans, animals - or whatever strikes the imagination. Known as karsts, these limestone formations span southern Asia, from the Philippines to China, where they have inspired painters from time immemorial.¿ Here in Vietnam, clad in dense foliage and honeycombed with a labyrinth of caverns, the islands rise from the sea like gigantic sentinels who, according to legend, have defended this land for millennia.