The fabled rivers of Europe, rich with looming castles, shore-side vineyards and romantic cafés, remain the special domain of very small vessels. Among the premium and luxury cruise lines plying the Rhine, the Rhone, the Danube, the Seine and other great European waterways, Viking River Cruises set the standard, and it set it high. The world’s largest river cruise line, Viking has more than one dozen ships based in Europe, including no fewer than six longships launched this year. Viking’s hallmark longships each carry 190 passengers, all in outside-facing cabins, and each European sailing includes guided shore excursions, onboard lectures and open-seat dining with regional specialties and complimentary wines. Viking’s Explorer Suites, two on each longship, are the largest on Europe’s rivers. It’s not surprising many passengers consider Viking’s river cruises an experience of sheer luxury, although its fares are quite affordable.

Meanwhile, fully half a dozen luxury river cruise lines, focusing on North American passengers, are stepping up efforts to outdo Viking. AmaWaterways, the first line to offer two-balcony cabins, a fleet of bicycles and a specialty restaurant, is highly regarded for its wine cruises and Christmas market sailings; its three dozen luxury riverboats each carry fewer passengers than Viking’s longships. A second rival, Avalon Waterways, boasts the youngest fleet in Europe, and its two newest ships, both launched this year, come with an extraordinary number of small suites. The Avalon Imagery II has 52 suites and 12 staterooms; the larger Avalon Passion features 67 suites and 16 staterooms. In the suites, glass walls retract to create “open-air balconies.”

Another luxury riverboat line, Scenic, is known for its Space Ships, so named to emphasize their spacious cabins and public areas. Scenic includes tips, tours and drinks in its fare, as well as a fleet of bicycles with electric motors and private butler service for each stateroom. In 2017 Scenic will introduce Scenic Culinaire on its Bordeaux and Rhone cruises, an onboard cooking class with local ingredients, cooking stations and a cheese and wine cellar.

Tauck River Cruises, known for the “relaxed elegance” of its small European ships, will launch its newest vessel, the 130-passenger MS Joy, in 2017. The Joy offers the most space per guest of any European riverboat, with 22 suites measuring 300 square feet and eight two-story loft cabins. Not to be outdone, Uniworld launched the Danube River-based SS Maria Theresa in 2015. This ornate 150-passenger vessel, dubbed by Uniworld president Guy Young a “floating castle,” boasts regal, 18th-century-style interiors. Moving ahead, Uniworld will launch another elegant, all-inclusive super-riverboat in 2017, the 128-passenger Joie de Vivre, for cruising the Seine River from Paris to Normandy.

And there’s more. Crystal Cruises created Crystal River Cruises as its entry into the crowded waterways of Europe. This year marks the inaugural sailings of the 154-guest, all-suite Crystal Mozart, the only riverboat with a full wrap-around promenade. The Crystal Mozart currently waltzes its guests up and down the Danube River. And in 2017 and 2018 Crystal will debut no fewer than four more ultra-luxury riverboats. No doubt Crystal’s rivals, including Viking, can be counted on to add yet more high-end vessels to the interiors of Europe, a region said to have more navigable rivers than any other in the world.