We could have flown, of course. There would be an orderly line at immigration and a taxi waiting to whisk us to the hotel. The whole trip would've taken roughly an hour, and we'd be poolside by noon. It would've spared us from a whole lot of my son's “Are we there yet?” whining. But where's the thrill in that? So in the half-light of a hazy winter morning, bleary-eyed after the sleepless overnight train ride from our home in Bangkok to Vientiane, my wife, our five-year-old son, and I crossed the Mekong into Laos on a clattering railway carriage. Aside from a single hotel reservation in Luang Prabang, Laos's former royal capital, we had no plans nor even a return ticket. We had embarked on this unscripted adventure in the hopes of channeling the halcyon days of our first visit to the country, a free-wheeling backpacking trip more than 10 years ago. It was a way, we figured, to instill our son with a similar thirst for adventure.…