New £1.3bn Legend of the Seas liner has a zip-line, giant waterpark and TRAIN at sea plus room for 7,000 passengers - but is this floating goliath actually fun to holiday on?

Brand new Royal Caribbean mega liner stretches almost a quarter of a mile long
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Some things about travel are hard to get your head around, particularly when it comes to cruising.

Big ships with rollercoasters, zip-lines and aqua parks are now the norm, but how about one with a train? Well, I’ve just got on a new ship which has exactly that – a station, two platforms and a pair of locomotives.

Yep, you can hop on a train while mid-Med. How crazy is that?

Of course this is no ordinary ship. It’s Legend Of The Seas, the newest addition to Royal Caribbean’s family-friendly fleet, coming in at the eye-watering cost of £1.3 billion, and I’ve been invited to a preview four-day cruise ahead of its maiden voyage.

For the first time, the line is launching one of its mega-ships in Europe instead of the US, and we’ll be sailing from Malaga to Rome.

It's a whopper! Set to launch this summer, the Legend of the Seas from Royal Caribbean can carry 7,000 passengers and tries to tick every box, with a global menu and shows that are 'West End meets Cirque du Soleil'

Legend is a 20-deck colossus which is now officially (by a smidgen of a foot) the biggest cruise ship in the world. It can carry 7,000 passengers, is topped by a glass dome heavier than a Boeing 747 and trumps its two sister ships (Icon Of The Seas and Star Of The Seas) by having its very own railway, more of which later.

Royal Caribbean is constantly innovating, evolving and dreaming up ideas to ensure that no two ships are exact replicas – you find fresh offerings on each one.

Take my family cabin. There’s a wall-size chalk board next to the kids’ sleeping quarters – cutesy bunkbeds that are cordoned off by a curtain.

It would have been a great way to communicate with my children had they been with me. Instead, I chalk messages to my stewardess, Nancy from Trinidad and Tobago.

Thank you for this, may I have more of that, hope you had a nice day and so on. ‘I appreciate you,’ she messages back.

Jo Kessel went aboard to check out this colourful floating city, which has water slides galore, a train experience and a zip-line at sea

Then there’s the ship’s rubber duck-inspired carousel. Don’t imagine it’s reserved for under-tens. Grown-ups love it too. I ride a particularly endearing orange duck on repeat, half-expecting (and longing) to take off Mary Poppins-style.

Legend is no shrinking violet. It’s bright and bold, especially the upper decks, with its tangle of colourful water slides. But it’s also unexpectedly artsy and classy.

Dotted around the ship are showstopper sculptures that will have you reaching for your camera: a red British telephone box cinched in at the waist, and a female swimmer dangling on a diving board. And then there’s The Pearl, a giant kinetic walk-through clamshell illuminated by ever-changing lights.

If you like seeing, tasting and experiencing things you never have before, then Legend is for you. When it comes to cuisine there’s Korean, Mexican, Cajun, pizzerias – you name it, all at no extra cost. Ditto the ship’s shows, which are West End meets Cirque du Soleil, only on steroids.

I take in two new productions on the first night. Shockwave is the first, an aqua show packed with high somersaulting dives and aerial ballerinas.

At one point a drone butterfly flutters above the audience and a swimmer plummets (intentionally) from the top of a 55ft waterfall. It’s choreography like you’ve never seen before.

There are highly photogenic art pieces placed across the ship, to encourage guests to share their voyages on social media (Pictured: Jo with a twisted British red phone box)

Later, while watching the ship’s ice-skating show Fusion – yes, Legend has a rink guests can use during the day – I’m wowed by triple axels and headbanger spins. The storyline is themed around the elements, brought to life by animated projections.

By chance I’m sitting next to American 3D artist Shelly Boehm, who tells me she’s spent four months creating the water section of the show. I watch in wonder as her designs turn the ice into an ocean full of swimming turtles and waving coral.

It’s hard to convey quite how massive this leviathan is. At 1,200ft Legend is nearly a quarter of a mile long, and the ship’s been divided into neighbourhoods. One’s for families, another’s adults-only.

Then there’s the two-deck Royal Promenade and the exclusive Suite neighbourhood. You’ll need deep pockets to stay here. Off-season the three-storey family townhouse will set you back about £60,000 a week.

The Pearl sits between deck 5 and 6 and actually has a critical role - to hold up the liner's central structure...but Royal Caribbean has also managed to turn it into a photo opp

Everyone soon finds their preferred ’hoods, and mine are Central Park, a leafy district with real plants and Park Cafe’s bagel bar, and Thrill Island. This is home to the aqua park and high-octane rides.

There are waterslides as well as the heart-lurching Crown’s Edge, part freefall, part zip-line, which drops you 150ft over the ocean before whizzing you back round to the ship.

I pluck up the courage to do it, but my hands shake for hours afterwards. Do it again? Absolutely not!

Bold: The communal areas of the ship major on bright shades, with pops of colour everywhere you turn

If it all gets too much there are quiet spots to recover, such as the wraparound promenade on Deck 8 and Chill Island, where you’ll find the majority of the ship’s seven pools. Swim And Tonic’s my favourite, the largest swim-up bar at sea and the perfect place for a post-Crown’s Edge tipple.

While most of the offerings on Legend are included in the fare, some do cost extra, the train being one of them. And it’s time to come clean. This isn’t Royal Caribbean’s answer to the Orient Express – instead it’s a VR ride.

The carriages themselves look genuine, but their movements and soundtrack are simulated, as are the visuals outside the window.

My 90-minute journey comes with a five-course dinner and takes us along the ancient Silk Route from China to Venice via India and Turkey.

Each destination is paired with its national cuisine and scenery: think pandas outside the window as we tuck in to dim sum, and Turkish lamb chops as we rattle past Cappadocia. It’s a great evening and the food is delicious.

An even more elegant and glitzier affair is the ship’s new Hollywoodland Supper Club, which oozes with the glamour of golden-age Tinseltown. Food and libations are paired with jazz standards performed by a live quartet – a brilliant concept.

It turns out that blinis and caviar go perfectly with a Sunset Martini and the Pink Panther theme tune. There are eight cocktails and courses in total – all delicious – and the vibe is slinky, sensual and starlit. It’s worth the extra splurge for the drinks alone.

While these two exclusive dining experiences do cost extra – £144pp for the train, £190pp for the Supper Club – you do not need to pay a penny more than your cruise fare to have a good time.

And even though it’s impossible to cover everything in four days, I manage to squeeze in Legend’s final new show, a 90-minute production of Charlie And The Chocolate Factory.

Oliver, age 11 (yes, a child actor) is awesome in the title role and the special effects are off the scale. At one point the smell of chocolate wafts across the theatre while the audience sniffs in disbelief.

It is this attention to detail that sets Legend Of The Seas apart. And with so much entertainment, there really is something for everybody.

Legend will be sailing in the Mediterranean all summer and you are guaranteed a legendary voyage on a ship that not only lives up to its hype but to its name as well.