Potential travelers should be aware of the energy level and mobility required to see Angkor Wat and its associated ruins; to venture into local religious sites and markets, and to visit people who live near the rivers. You don’t need to be an athlete — short strenuous hikes were few and Avalon provided transportation for those who did not feel up to them — but if you lacked stamina or could not get around relatively well, you would miss part of this trip. Perhaps that’s why the passenger list was young for a river voyage, ages from early 30s to 70s.

Cambodia and Vietnam have become a hot river cruise destination because of such Bucket List destinations as Angkor, which was home 1,000 years ago to a great Hindu empire that left behind some 19 square miles of stone temples and tombs, now in various states of ruin and restoration; the bustling cities of Siem Reap, Phnom Penh, and Ho Chi Minh; the Cu Chi Tunnels in Vietnam where the Viet Cong hid during the war that lasted deep into the 1970s; and the majestic Mekong River.

The wide Mekong begins in Tibet and flows through China, Laos, and Cambodia before reaching Vietnam’s delta, providing power, food, irrigation, and transportation for millions.

The most popular itinerary is between Siem Reap, which is a short bus ride from the Angkor sites, and Ho Chi Minh City, a motorbike-mad metropolis that almost makes you forget that you are in communist country — until you run across a picture or statue or sign with the name Ho Chi Minh, a frequent occurrence.

River cruise lines — including AmaWaterways, Viking River Cruises, Vantage and Aqua Expeditions beginning in 2014 — also operate cruises on the Mekong and tributaries between the two cities and are adding new, modern riverboats to their fleets.

Siem Reap is not on a waterway, so on most tours, the first day out of Siem Reap is a long bus ride around Tonle Sap Lake to reach the Tonle Sap River, where riverboats await for a cruise to the Mekong and then on to Ho Chi Minh City.

Avalon Waterways’ new Avalon Angkor is designed with a shallower draft — the vessel needs only about 4 feet 7 inches of water — so it can cross Tonle Sap Lake in the wet season on cruises from July through early January. That’s when the lake and river are awash in water, backed up from a flooding Mekong downstream. From mid-January to June, passengers will spend at least several hours on a bus getting around the lake.

My February river cruise included the bus ride. We met the Avalon Angkor at Prek Dam, Cambodia, where it was tied to a tree at the bottom of a sloping embankment. We climbed down a series of crude steps hollowed out of the dirt and lined by crew members ready to assist anyone needing a steady arm.

In the next seven days, passengers from the United States, Canada, Australia, and the United Kingdom visited temples, villages, outdoor markets and museums.

Highlights were making spring rolls in a cooking class; perusing American-made pictures at the Vietnam War Remnants Museum; a contest of bargaining in Vietnamese for specific treasure hunt items at an outdoor food market; and getting down on our knees to crawl through one of the Cu Chi tunnels.

David Molyneaux writes monthly about cruising. He is editor of TheTravelMavens.com