7. Kenai River (United States)
Scenic beauty: 4 | Nature and wildlife: 5 | Culture: 1 | Adventure: 4 | Activity options: 3
Running 82 miles through southern Alaska's Kenai Peninsula, this meltwater river is the most popular sport fishing destination in the state.
Each year there are two salmon runs, which also attract American brown (grizzly) bears along with moose, black bears and multiple bird species.
Beluga whales have also been sighted as far as six miles upstream in the spring.
A scenic, three-hour drive from Anchorage, the Kenai is all geared up for tourism should you fancy opting for a "drifting" wildlife safari, guided glacier walk or multi-day kayaking adventure.
6. Irrawaddy River (Myanmar)
Scenic beauty: 3 | Nature and wildlife: 3 | Culture: 5 | Adventure: 4 | Activity options: 2
If you've already seen the sights along Southeast Asia's majestic Mekong or missed the party in Vang Vieng, Laos' notorious river tubing party hub, consider a trip to neighboring Myanmar, where river tourism is taking off in the wake of the nation's democratic reforms.
Several international companies now offer river cruises on Myanmar's mysterious Irrawaddy River with varying itineraries taking in ancient temples, remote villages, local trading centers and important Buddhist sites.
5. Danube and Rhine (Europe)
Scenic beauty: 5 | Nature and wildlife: 2 | Culture: 5 | Adventure: 3 | Activity options: 2
The first European river cruises were on the Danube and the Rhine, and for good reason.
Connected by a canal system, the two rivers gurgle through 12 countries between them, with baroque cathedrals, medieval towns and romantic castles a-plenty scattered along their banks.
It's possible to see the most famous section of the Rhine -- between the Middle Rhine towns of Bonn and Bingen -- by ferry in as little as a day if you're pushed for time, though Danube highlights including the city of Melk in Austria, Bratislava in Slovakia, Budapest in Hungary and Vidin in Bulgaria beg for a longer expedition.
4. Sepik River (Papua New Guinea, Indonesia)
Scenic beauty: 3 | Nature and wildlife: 3 | Culture: 5 | Adventure: 5 | Activity options: 2
Referred to as the Amazon of the Asia-Pacific, Papua New Guinea's Sepik River is among the world's most diverse ecosystems.
Winding through alpine heaths, dense tropical rainforests and mangrove swamps before emptying into North PNG's Bismarck Sea, this largely unchartered waterway reaches deep into a world that has remained virtually unchanged for centuries.
River cruises offer an insight into the culture of local communities living so primitively that many old timers can still recall the taste of human flesh from their headhunting days.
3. Río Cahabón (Guatemala)
Scenic beauty: 4 | Nature and wildlife: 3 | Culture: 2 | Adventure: 5 | Activity options: 5
Never heard of it? Few had, until a few years back, when a section of the Rio Cahabón's densely forested pathway through central Guatemala was forged as a key stop on the Central American backpacker trail.
Known as Semuc Champey, the series of spectacular steeped limestone pools bridging over the river are accessed via a hiking trail near the village of Lanquin.
Local hostels also offer tubing excursions along the Rio Cahabón's tributaries, candlelight tours of a cave system carved out by the water, and year-round grade III and IV rafting.