If you were told to design a playground for adults, and given the freedom to be as creative and far fetched as you liked, even then what you came up with may not be as utterly imaginative as this place.

No Man's Fort is one of three man-made islands off the coast of Portsmouth, built in the 1860s to help protect Britain from the rumoured arrival of Napoleon III and his French army, and also manned during the Second World War.

Now a luxury adults-only hotel, after being purchased from the MoD and opened in its current use in 2012, the fort boasts 22 bedrooms, a bar, restaurant, sauna, large seating area in the centre, plus an outdoor area complete with hot tubs.

There is also Spitbank Fort (smaller than No Man's) and Horsesand Fort, the latter of which is being preserved in its original state and is due to open as a museum in August 2016.

Trips to these historic structures are organised by Solent Forts, who promise a memorable experience to all who set sail for the forts – and I can't think of anyone who would disagree with that sales pitch.

Joining us on the boat into the Solent were other couples, a family who had splashed out on a birthday present for one of their young adult children and (from overhearing conversation) wealthy types who had seen their fair share of private parties in exclusive locations. The fort experience has enough to fascinate people from almost any background you can think of.

So, along with our diverse group of equally excited adventurers, the boat took us out to No Man's Fort on what was a gloriously sunny day in February. Good job too, as trips can be cancelled in stormy weather.

SEE ALSO: Castle Leslie Estate: An Irish retreat 'a million miles from anywhere'

As we prepared to disembark onto the island, you could see why this was the case, as the boat bobbed around while it was – very skillfully it must be said – tethered to the railings, even on the calm waters of that day.

Prepare for an experience

Our break being the aptly-named Fort Break Experience, we were welcomed onto the triumph of Victorian engineering with a glass of bubbly and invited to relax in the lobby area.

Although it is not cheap, I would really recommend the Experience package as a way of making the most of your stay.

Plenty of food and drink is handed to as you work through a neatly arranged itinerary, including being taken on a tour in small groups, and it provides a pleasingly laid back structure to the day.

But don't worry, relaxing and freedom to explore the unique surroundings is a large part of this, and each part is optional, so there is no danger of feeling like you are being ruled by a strict timetable.

The unique setting of No Man's Fort

After learning some cool facts about the fort during the short tour, great for getting a feel for its history and to have in the bank to impress friends and family with later, a buffet lunch is served before a period of free time to do as you wish.

To return to the playground analogy, there is a childish excitement during these moments where you are urged to explore any part of the fort you like.

Want to go up the lighthouse? Sure. Grab a drink and play some pool? Why not? You can even play laser tag in the corridors where serving soldiers once defended the country for goodness' sake!

Next on the itinerary of dreams was tea and cake - and this was where we decided to exercise the freedom afforded to guests to great effect. Still full from lunch, and safe in the knowledge that a substantial dinner awaited in but a few hours, we stole a march on those heading down for the edible treats to instead claim a place in one of the two hot tubs on the roof.

What a decision that turned out to be, as we had just enough time to get suitably placid before being treated to a magnificent sunset over the Isle of Wight.

An unforgettable stay

Evening inevitably arrived, and with it the promised three-course meal. Given the fact that the fort setting is enough to balance out almost any shortcomings in other areas, the hotel would be forgiven for serving up only half decent food, but yet again what's on offer is stunning. The beef fillet and poached lemon dessert were particular highlights.

With darkness now upon us, there was still time to retire to the bar – complete with stylish glowing tables – and then to the roof once more for rum hot chocolate and toasted marshmallows around a fire pit.

It's so easy to forget that you are perched on top of effectively a granite and stone dinghy, with waves lapping at the sides, at such times.

Our junior suite room

Then, to bed. The whole island has a very compact feel to it so it is a surprise to walk into your bedroom to find it is impressively large, with his and hers sinks in the bathroom.

Of course, going to bed is also optional. If you wanted, you could jump back into the hot tubs for a midnight dip, which one family gleefully did.

After a great breakfast the next morning, the time had sadly come to leave. In keeping with the intimate feel of the whole fort, the staff, who make every effort throughout your stay to make you feel welcome, wave you off as the boat leaves as if you were dear friends – a nice touch and further proof of the attention to detail by Solent Forts.

While this might read as quite a gushing review, I would imagine every one of our fellow passengers would have felt the same as they left No Man's Fort.

We left buzzing about the unforgettable experience and would recommend it as a special treat or for a big occasion where you don't mind splashing out.

Factbox

Pete's stay was courtesy of Solent Forts and was the Fort Break Experience package priced from £800 per night for two people. This includes return boat trip, lunch, tour, dinner, breakfast and use of facilities.

To book, visit www.solentforts.com , call 023 9298 4806 or pop into the office in Gunwharf Quays, Portsmouth.