Spine-tingling slides and race tracks with hairpin turns aren't only found at theme parks anymore. And unusual spas don't just pop up on land.
As it happens, passengers are shelling out millions to spend their vacations on over-the-top cruise ship experiences. For their part, cruise lines are happy to oblige, pampering and thrilling passengers with snow, butlers and race tracks — all on the high seas.
With data showing more American workers are leaving increasing amounts of unused vacation time on the table, CNBC surveyed the travel industry to discover which offbeat destinations might entice would-be travelers into taking time off.
Snow on a ship
On their small (930 guests, max) ocean cruise ships, Viking Cruises hews to the line's Nordic Heritage. Ship interiors have a modern and elegant Scandinavian design, and there's plenty of aquavit in the bars, Scandinavian-inspired dishes on the menus and Nordic artwork on the walls.
Each ship also has its own Viking Heritage Exhibit and a spa reflecting the centuries-old sauna tradition, complete with a very chilly "snow grotto" where real snowflakes fall from the ceiling.
Salty therapy
Scenic's all-inclusive river ship cruises come with personal butlers, complimentary beverages and a long list of other extras. But there are some bonus amenities on two of Scenic's recently-redesigned France-based "Space Ships:" The Scenic Diamond, which visits the rivers of Bordeaux, and the Scenic Sapphire, which cruises on the Rhône and Saône in the south of France.
Each sports an on-board cooking school (with a cheese and wine cellar) and a therapeutic salt lounge. The bricks are designed to recreate the energizing micro-climate created by the negatively-charged ions found in salt caverns.
Eye in the ocean's sky
Passengers on Royal Caribbean's Quantum Class Ships can take a complimentary 15-minute spin in North Star — a glass observation capsule Guinness World Records has declared to be the "Highest Viewing Deck on a Cruise Ship."
The 14-passenger pod goes up 300 feet in the air and rotates out over the sides of the ships, offering unique and exhilarating views in port and at sea. Private North Star flights are also available.
Finding Nemo
Complimentary water sports equipment and amenities on Crystal Cruises' Crystal Esprit yacht include jet skis, kayaks and paddle boards. For an extra fee ($599/per person for 30 minutes), passengers can join a pilot and another guest inside a 3-person pressure-controlled submarine, or diving cabin.
"It's an amazing opportunity for guests to explore life under the sea in the Seychelles and West Indies, and fully embrace life at sea," said CruiseCritic.com's Colleen McDaniel.
A really big clipper
Star Clippers' five-masted, full-rigged 439-foot Royal Clipper looks like an old-fashioned sailing ship. Tucked inside are modern navigation systems, upscale accommodations and amenities, such as three swimming pools and supervised mast-climbing. The spa, health club and other areas of the ship's Captain Nemo Lounge even have underwater glass portholes.
When Star Clippers' Flying Clipper, debuts in Fall 2018, "It will feature an 18-foot-deep dive pool spanning spans the depth of two decks, with glass sides so passengers are able to watch the divers in the water," says Colleen McDaniel, Senior Executive Editor of CruiseCritic.com, "And the ship will offer diving course with the ship's Dive Master and with local instructors in various ports."
The $6 million bartender
If you've bellied up to one of the Bionic Bars aboard some of Royal Caribbean cruise ships, there's no need to try to catch the eye of the bartender. Guests simply place their drink order on a tablet and then the robotic art bartenders swing into gear, mixing up 2 drinks per minute and up to 1000 drinks a day.
Slide into the ultimate abyss
On Royal Caribbean's giant Harmony of the Seas and, soon, on its even larger Symphony of the Seas cruise ship, guests willingly enter the mouth of this fishy-looking creature for the thrill of being plunging 10 stories - in the dark - on the Ultimate Abyss, touted as the tallest dry slide at sea.
Race track at sea
When Norwegian Cruise Lines' Norwegian Bliss arrives in May 2018, passengers will be able to play galactic-themed laser tag or race electric cars at up to 30 mph on a 1,000-foot long, two-level race track that will lay claim to the title of largest race track at sea. Worried about the noise? The electric race cars will be silent, but each driver will have roaring engine sounds piped into their helmet headsets.