There must be some rule in Laos that says the further south you go the more relaxed it becomes, because just when you thought your blood pressure couldn’t drop any more, you arrive in Si Phan Don… The name literally means ‘Four Thousand Islands’, and the few you are likely to visit on this scenic 50km-long stretch of the Mekong are so chilled you’re ­liable to turn into a hammock-bound icicle.