The cruise trend that will leave you feeling, hot, cold and relaxed

Ships have always moved between hot and cold climates, from sweltering in Singapore to shivering in Alaska, before burning in Barbados, then freezing in the fjords of Greenland.

The same concept is offered in the spa. Contrast therapy is the hottest (and coolest) wellness trend at sea.

Before I ever went to Norway or Finland, I experienced a Scandinavian bathing ritual in Viking Cruises' Nordic Spa. This complimentary facility is renowned for its snow grotto.

After relaxing in the sauna, dipping into the cold plunge pool and warming up again, you enter a glass-enclosed room where manmade snow falls from the ceiling. Viking's expedition vessels also have a badestamp (wood-sided hot tub) positioned next to a half-open window so you can feel simultaneous hot and cold sensations.

Scenic Eclipse's Senses Spa is the other standout, with complimentary facilities including an ice corner, salt therapy lounge with heated lounges, and infrared sauna seats that soothe your back while you read a book. I spent a whole afternoon in this thermal sanctuary.

MSC Cruises' Aurea Spa has the Kneipp walk, where you step barefoot through alternating pools of hot and cold water, or a vertical version via shower jets.

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The latest spa treatments are cryotherapy-inspired. Crystal Cruises' LED and Cryo Facial is apparently good for jet lag. I also had a lovely facial on Swan Hellenic's Minerva, where various chilled devices were rolled over my face while I snoozed on a heated bed.

Celebrity Edge-class ships have quartz beds filled with warm sand that conforms to your body to relieve muscle tension.

But the best massage I ever had was Princess Cruises' R3 Pain Management Therapy, which uses hot packs and cooling balms to unravel the mysterious knots of your aching back.

If spa treatments are not in your budget, you can DIY in your cabin's bathroom by trying to figure out how to work the hot and cold shower taps. As easy as cracking the code on a bank vault.

The most extreme contrast therapy is combining a sauna session with a polar plunge - jumping off the ship into Arctic or Antarctic waters.

That's not my cup of (iced) tea. A doctor is always on standby, which seems less like reassurance and more like a clue.