River cruises are gaining popularity every year as a way to explore Europe as well as some of the more exotic regions of the world, like Vietnam and Cambodia, or Myanmar. River cruises are for travelers who like to explore in comfort, while unpacking only once. While river cruising might feel slow, the pace is fast, with ships visiting a port or two every day.

Many cruise lines offer outstanding river cruises. The biggest name in river cruising might be Viking, which really was an industry pioneer. Viking, open to adults only, offers cruises on its innovative Longships, designed to give passengers more balconies as well as more outdoor space. AmaWaterways is another big name in river cruising, offering modern spaces and programming created to lure those who value wellness and fitness as well as families. Avalon Waterways offers unique cabins, with beds facing the windows or balconies so you won't miss a thing while sailing.

Summertime, particularly July and August are ideal for river cruises. The weather in Europe is warm and pleasant, allowing passengers to enjoy the outdoor spaces onboard the ships and comfortably explore ports. If you can tolerate some colder weather, December is perfect for exploring Europe and visiting its wonderful Christmas Markets, which take place in towns and cities along the Danube and Rhine rivers as well as the French waterways. It's a great way to enjoy souvenir shopping while sipping mugs of warm, spiced wine.

River ships are much smaller than ocean ships, with those sailing on the Danube and Rhine rivers measuring 443 feet long. Most are four decks or smaller. River cruising also has a more casual approach to virtually every aspect of a sailing. The dress code for river cruises is more casual, with no formal nights; shore excursions might be organized with a paper signup system; and getting on or off the ship can be done in seconds. River cruising tends to be fairly inclusive, too, with many cruise lines including at least one shore excursion in every port, wine, beer and soda at meal time and free Wi-Fi. Because they're small, river cruise ships don't have features like casinos, theaters or kids clubs.

Most river cruise ships range from about 140 passengers to just under 200. That means you'll quickly get to know your fellow passengers, as meals are shared in only one or two restaurants, and drinks take place in one lounge. Fewer passengers also means smaller groups ashore for shore excursions.

The most-popular rivers for cruising are the Danube and Rhine rivers in Europe. These cruises visit towns in Germany, France, Austria and Hungary, among others. Some river cruises visit the French waterways, including the Seine and Rhone rivers. The Douro River in Portugal is gaining in popularity, as more cruise lines are building ships to explore the unique countryside. Many cruise lines also offer cruises on more exotic rivers like the Nile, Irrawaddy, Mekong and Volga.

River cruising is also a great way to explore the United States, with itineraries on rivers including the Mississippi, Ohio, Columbia and Snake. Many of these river ships are inspired by the old paddlewheelers and are often decked out in Victorian decor.

Prices for river cruises start at around $300 per person per night but can stretch to $500 or more, depending on the inclusivity of the cruise line, the time of year and destination. Cruises on the Danube and Rhine generally run seven days. Many river cruise lines regularly offer deals aimed at solo travelers; these sales might reduce or eliminate the "single supplement," a hefty fee solo travelers often are required to pay.