Halong bay is north of Hanoi and a registered World Heritage site. A fantastic place of huge rocky islands called ‘karsts’ that jutt up out of the bay, thousands of them, all trying to out do each other in size or sheer magnificence. Even though it is flooded with tourists in April when I went, it is so vast that, once taken by boat from the teeming port, you soon lose sight of the hundreds of boats that regularly ply the green waters of the bay. It is other-worldly, eerie, the day I went was overcast, but it had an incredible feeling of vastness and strangeness, like you had been transported to some other planet, a watery world made up of strange rocky shapes gesticulating at the sky. The great karsts themselves, I was told, took around twenty million years to form in the muggy tropical climate of northern Vietnam. A must for any visit to South East Asia.