Shopping in Singapore, looking down from the Twin Towers in Kuala Lumpur, taking in the massive ancient temples in Cambodia’s Angkor Wat and Borobudur on Java: Tropical Southeast Asia is hardly short of things to do for tourists or places to go. Some of the region’s best attractions are not on land or even above the sea-level, however. Diving is another reason Southeast Asia is popular with tourists, and East Timor, Raja Ampat in Indonesia, Thailand’s Similan Islands and Sipadan near Malaysian Borneo are among the world’s best-regarded locations. But the region arguably even has untapped poten…