From the Chiang Khong district in extreme northern Thailand, very near the point at which the borders with Myanmar and Laos meet, my tour group left Thailand, took a bus across the Fourth Thai-Laos Friendship Bridge to enter Laos, got our visas, then boarded a Laotian slow boat (that's the actual name for the type of boat, not a criticism!) for a two-day journey down the Mekong River, staying overnight in a guesthouse in tiny Muang Pakbèng before arriving at the river port in Luang Prabang the next day. In all, it was approximately 120 KM and around 12 total hours in the boat.
The cruise was smooth and relaxing and filled with one amazing sight after the next: thick jungle, rolling hills, rice paddies of many varieties*, fishermen, villages, farms, livestock, local ferries (small boats with high speed motors: see the section on Laos Fast Boats at the bottom of this page), Chinese high speed train line construction**, limestone karst formations, fog-shrouded mountains, spectacular rain showers and thunderstorms, and even a couple of elephants.
*Did you know that some types of rice can be grown on the steep slopes of hills (and I don't mean via use of terracing) instead of traditional flat wetland field areas? I hadn't!
**Beijing is investing heavily in building more transportation links between western China and the waters and ports of Thailand and Malaysia. The Fourth Friendship bridge and the highway being planned in the area are also part of that investment.