After a terrifyingly choppy five-hour ferry trip across the Strait of Malacca from Malaysia, then a lost number of hours with a minibus driver negotiating dusty, potholed roads at top speed, I eventually started my exploration of Sumatra in Bukit Lawang. Here, thanks to the Bohorok orang-utan reintroduction centre, backpacker cafes and guesthouses once lined the riverbanks, until almost the entire town was destroyed by a flash flood one night in 2003.