Even if you own a fabulous private yacht, it simply may not be possible to sail it to every corner of the world (for example, the Amazon?). Said yacht also may not be outfitted with a casino, a five-star spa, multiple gourmet dining rooms, or a nightclub just for your teens—nice things to have when traveling with family and friends.

Regardless the reason, there’s never been a better time to book a sail aboard an ultra-luxury cruise ship. Both Silversea Cruises and The Yachts of Seabourn have debuted brand new ships in the past year; Seabourn’s second new build in as many years takes to the seas this summer (with a third lined up for launch spring 2011). Additionally, Crystal Cruises (which gets our vote as best line for families) gave its already-stunning Crystal Symphony a $25 million makeover last fall.

And, should you desire to sail the Amazon (in luxury, of course), the best way to do so is with Peru-based Aqua Expeditions, which launched its 24-passenger ship two years ago. Its second vessel, the 16-suite M/V Aria, is currently under construction and will launch in April 2011.

And by all means, should you prefer the privacy of your very own yacht, these ultra-luxury liners are all available for private charter. Following is a look at the new (and newly improved) luxury ships to consider sailing on this summer and beyond:

Aqua Expeditions

Amazon and luxury are not always words you hear used together, but that changed two years ago when Peru-based Aqua Expeditions launched its 24-passenger, 130-foot M/V Aqua, designed to showcase the best of the region in serious style. The ship’s instant success has resulted in the construction of a second ship, the 147-foot M/V Aria, set to launch next April.

Guests onboard the Aqua Expedition ships—the brainchild of businessman Francesco Galli Zugaro—enjoy daily water-based excursions to experience such wonders as pink dolphins and six-foot-wide water lilies; other activities include floating on black water rivers, fishing for sharp-toothed piranhas, and interacting with the locals in remote villages. Many of the onboard guides grew up in Amazonia and regale guests with tales of life and folklore about little-visited areas such as the remote Pacaya Samiria Reserve. Twice the size of Yellowstone National Park, the Reserve is located on the headwaters of the Amazon basin and spans more than five million acres.

The voyages depart year-round out of Iquitos, Peru (a 90-minute flight from Lima), and offer three-, four- and seven-day itineraries. The guest suites measure about 250 square feet and feature large panoramic windows and en suite sitting areas. All suites are air-conditioned, with the ability to interconnect up to four (ideal for families). The Aria will be slightly larger, with 16 stylishly designed suites accommodating 32 passengers. It will also feature an outdoor Jacuzzi, an exercise room, and a reference library.

Befitting the ambience of a five-star boutique hotel, all meals on board both ships are highlighted by fresh, delicious Peruvian fare—created in partnership with Pedro Miguel Schiaffino, one of Peru’s top 10 chefs. Complimentary South American wines are paired with dinners each evening.