Tastes on the open seas are shifting to favor minimalist decor over the ornate, interest in sustainability is slowly growing, and designers report that yacht owners are adding more bells and whistles to their floating residences than in their real homes.

If planes are where we carve out cozy personal spaces as we hurtle from point A to B, yachts are all about the journey—expansive, floating residences that should feel like a vacation home you never want to leave. “In the past, kings and princes ruled their castles,” says Giovanna Vitelli, vice president of Azimut Benetti Group, the world's largest manufacturer of megayachts. “Today, boats are the contemporary castles—there is no limit to what you can do with them.”

Headquartered in Avigliana, Italy, Azimut Benetti Group comprises several sub-companies, including two—Azimut Yachts and Benetti Yachts—with boats that retail for anywhere from $600,000 to $400 million and range from 34 to 350-plus feet. (A quick primer for the uninitiated: Vessels over 80 feet are considered megayachts; superyachts are 100 feet and up; and gigayachts more than 300 feet.) From sweeping floor-to-ceiling windows—Azimut Yachts says it was the first brand to break from old-fashioned porthole windows—and trappings like diving centers, Jet Skis and helipads, tricking out yachts of this scale requires pushing the limits of imagination.